ASA 5505 9.1 and NAT issues to single dynamic IP

Question

Good afternoon everybody, 
a few days ago I tried setting up my ASA 5505 to allow access from the outside network to an Exchange server (ports HTTPS and SMTP) in my inside LAN.
Everything seems to be working... until my outside IP address changes (for example due to a router reset or a disconnection caused by the ISP). 
As soon as the outside address changes the NAT rules are deleted and these 2 lines pop up in the syslog :
<166>%ASA-6-305012: Teardown static TCP translation from inside:192.168.1.150/25 to outside:79.6.105.13/25 duration 0:01:17.
<166>%ASA-6-305012: Teardown static TCP translation from inside:192.168.1.150/443 to outside:79.6.105.13/443 duration 0:01:17.
In the same time, the consolle connection shows these two messages :
Asa5505# ERROR: NAT unable to reserve ports.
ERROR: NAT unable to reserve ports.
I have moved both Anyconnect VPN essentials and http ports to 10443 and 8080 respectively so port 443 should be free for nat.
This is the configuration file, I  have marked the lines related to network objects and relative nat statements, I hope it helps to find out where's the problem.
Obviously the lines in red are the ones disappearing... I'm quite desperate, actually.
ASA Version 9.1(5) 
hostname Asa5505
domain-name home
enable password XXXXXX encrypted
names
interface Ethernet0/0
 description ADSLPPoE
 switchport access vlan 2
interface Ethernet0/1
 description Internal_LAN
interface Ethernet0/2
 description Management_Net 
 switchport access vlan 3
interface Ethernet0/3
 shutdown
interface Ethernet0/4
 shutdown
interface Ethernet0/5
 description Uplink
 switchport trunk allowed vlan 1,3
 switchport trunk native vlan 1
 switchport mode trunk
interface Ethernet0/6
 description Wireless-POE
 switchport trunk allowed vlan 1,3
 switchport trunk native vlan 1
 switchport mode trunk
interface Ethernet0/7
 description Webcam-POE 
interface Vlan1
 nameif inside
 security-level 100
 ip address 192.168.1.250 255.255.255.0 
interface Vlan2
 nameif outside
 security-level 0
 pppoe client vpdn group AliceADSL
 ip address pppoe setroute 
interface Vlan3
 no forward interface Vlan1
 nameif management
 security-level 100
 ip address 10.5.1.250 255.255.255.0 
ftp mode passive
clock timezone CEST 1
clock summer-time CEDT recurring last Sun Mar 2:00 last Sun Oct 3:00
dns domain-lookup inside
dns domain-lookup outside
dns server-group DefaultDNS
 name-server 192.168.1.4
 domain-name home
object network Exchange-HTTPS
 host 192.168.1.150
object network Exchange-SMTP
 host 192.168.1.150
object network Network_Inside
 subnet 192.168.1.0 255.255.255.0
object network Network_Management
 subnet 10.5.1.0 255.255.255.0
access-list Outside_ACL extended permit tcp any object Exchange-HTTPS eq https 
access-list Outside_ACL extended permit tcp any object Exchange-SMTP eq smtp 
pager lines 24
logging enable
logging asdm warnings
mtu inside 1500
mtu outside 1492
mtu management 1500
no failover
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
no arp permit-nonconnected
object network Exchange-HTTPS
 nat (inside,outside) static interface service tcp https https 
object network Exchange-SMTP
 nat (inside,outside) static interface service tcp smtp smtp 
object network Network_Inside
 nat (inside,outside) dynamic interface
object network Network_Management
 nat (management,outside) dynamic interface
access-group Outside_ACL in interface outside
timeout xlate 3:00:00
timeout pat-xlate 0:00:30
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00
timeout floating-conn 0:00:00
dynamic-access-policy-record DfltAccessPolicy
user-identity default-domain LOCAL
http server enable 8080
http 10.5.1.0 255.255.255.0 management
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart warmstart
crypto ipsec security-association pmtu-aging infinite
crypto ca trustpool policy
telnet timeout 5
ssh stricthostkeycheck
ssh timeout 5
ssh key-exchange group dh-group1-sha1
console timeout 0
management-access management
vpdn group AliceADSL request dialout pppoe
vpdn group AliceADSL localname aliceadsl
vpdn group AliceADSL ppp authentication pap
vpdn username aliceadsl password ***** store-local
dhcpd address 192.168.1.100-192.168.1.130 inside
dhcpd dns 192.168.1.4 192.168.1.150 interface inside
dhcpd wins 192.168.1.4 interface inside
dhcpd enable inside
dhcpd address 10.5.1.30-10.5.1.40 management
dhcpd dns 208.67.222.222 208.67.220.220 interface management
dhcpd enable management
threat-detection statistics access-list
no threat-detection statistics tcp-intercept
webvpn
 port 10443
 anyconnect-essentials
class-map inspection_default
 match default-inspection-traffic
policy-map type inspect dns preset_dns_map
 parameters
  message-length maximum client auto
  message-length maximum 512
policy-map global_policy
 class inspection_default
  inspect dns preset_dns_map 
  inspect ftp 
  inspect h323 h225 
  inspect h323 ras 
  inspect ip-options 
  inspect netbios 
  inspect rsh 
  inspect rtsp 
  inspect skinny  
  inspect esmtp 
  inspect sqlnet 
  inspect sunrpc 
  inspect tftp 
  inspect sip  
  inspect xdmcp 
service-policy global_policy global
prompt hostname context 
no call-home reporting anonymous
call-home
 profile CiscoTAC-1
  no active
  destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
  destination address email [email protected]
  destination transport-method http
  subscribe-to-alert-group diagnostic
  subscribe-to-alert-group environment
  subscribe-to-alert-group inventory periodic monthly
  subscribe-to-alert-group configuration periodic monthly
  subscribe-to-alert-group telemetry periodic daily
Cryptochecksum:XXXXXXXX
: end
no asdm history enable
Thanks in advance for your precious help !
C.

Answer 1

Update 29th of June :
Tried both suggestions: flashing to 9.22 didn't fix the problem. The only significant change between 9.1(5) and 9.2(2) is that as soon as I reload the configuration after a connection drop both nat rules are restored. In 9.1(5) the nat statements were removed from the runnning configuration when the PPPoE connection was lost, and the config was updated (or maybe saved?), so after a reload those statements were gone and I had to copy-paste them back in conf-t in order to restore them.
I tried using show xlate both before, during, and after the connection drop. As expected before the disconnection of PPPoE the static PAT rules are there, and the dynamic ones as well. During disconnection, all the xlate table is clean empty and the aforementioned error "Asa5505# ERROR: NAT unable to reserve ports. ERROR: NAT unable to reserve ports." pops up in the terminal. After a few minutes (needed by the DSL modem to perform its reset and bring up the DSL line again) the connection is established once more, but the only rules appearing in xlate are the ones created by the dynamic statements for management and LAN. If i reload the ASA using reload noconfirm every rule is restored and everything works again.
Two brief questions :
1) in my NAT statements for PAT, does it change anything if I modify them (for example) from 
nat (inside,outside) static interface service tcp https https
to
nat (inside,outside) dynamic interface service tcp https https 
? Since it seems like the dynamic PAT is restored after a connection drop I was asking myself what happens if I change the rules this way.
2) if there's not any ohter way to fix this, is it possible to schedule a reload of the ASA as soon as the PPPoE connection drops in order to make this problem "self fixing" ? I can't predict how many times a day the line drops and I can't be there 24/7 with my consolle cable connected in order to restore the nat statements ^^
Thank you for your precious help and patience !
C.