Strange behavior from script when dismounting content databases via PowerShell script

Question

So, this is my first time posting a question here.  I have taught myself PowerShell and for the most between friends, co-workers, or internet forums, I have been able to pick through most of the issues I have seen.  This one has me stuck. 
So, a little background, I have a script that goes through each web app in a farm, finds the database that hosts the root site, and detaches all other content databases from the farm.  It also writes a csv file so that a process can come along after the
fact to re-attach the databases.  I use this for patching so psconfig does not take quite as long as we have more than 50 content databases.  Here is the odd part.  After the first content database is detached, the second one is skipped, but
the remainder are detached.  So, I have two databases left per web app.  One that holds the root site and whatever the second database is after the first detach.  If I comment out the line that actually does the detach, this does not happen. 
Now, using ISE and adding break points, what I have found is that when I initially populate the array with the content databases ($var=$webapp.contentdatabase) all databases are in there.  When I start the foreach, all databases are in there.  Right
up to the point that I detach the first database, all databases are still in the array variable.  As soon as I detach that database, the database that I detached gets removed from the array.  It does this even if I set the variable to read only. 
It only happens with the first database detached in each web app.  I will try to explain this again with an example.  This test farm has 4 databases.  DB1, DB2, DB3, and DB4.  DB1 holds the root site.  The logic pulls the webapp info. 
It gets the URL of the webapp.  It takes that info and finds the site collection with that name (the root site).  Finds the database name from there.  It then gets a list of all databases in the webapp and starts to loop through.  So the
first one in the list is DB1.  It has the root site, so logic says do not delete.  It comes back to the loop with the next database DB2.  At this point, the array still has all 4 databases in the array.  DB2 does not host the root site,
so the logic gathers information and calls dismount-spcontentdatabase.  As soon as that is called, that database is removed from the array.  So, at this point, we have processes postion 0 and position 1 in the array.  Since the original position
1 has been removed, DB3 is now at postion 1.  So, the loop continues.  Sine we have now skipped DB3, we find DB4 and dismount.  Now, we have in the array DB1,DB3, and DB4.  My test environment has more and all are still there except for
the first one removed.  I have banged my head against the desk with this one.  If someone has some insight, I would appreciate it.
Here is the code that does it.
get-spwebapplication | foreach-object {
 $webapp=$_
 $waname=$webapp.displayname
 $waurl=$webapp.url
 $cdbs=$webapp.contentdatabases
 $rsite=get-spsite $waurl -erroraction silentlycontinue
 $rsitedb=$rsite.contentdatabase
 $rsitedbn=$rsitedb.name
 foreach ($cdb in $cdbs) {
  $cdbs=$cdbs2
  $cdbname=$cdb.name
  #Write-Host "$cdbname" -foregroundcolor red
  if ($cdbname -ne $rsitedbn) {
   $warn=$cdb.warningsitecount
   $max=$cdb.maximumsitecount
   $current=$cdb.currentsitecount
   $dbserver=$cdb.server
   Write-output "$waname,$cdbname,$dbserver,$warn,$max,$current" >> $outfile
   Write-host "dismounting $cdbname" -foregroundcolor green
   dismount-spcontentdatabase -identity $cdbname -confirm:$false
  else {
   Write-host "$cdbname holds root site. No action." -foregroundcolor yellow

Answer 1

what about keeping an array of all the non-root collections (may be database name) instead of dismounting them in the foreach loop of all the databases? After we have all the databases that need to be deleted, in a for loop starting with 0 and
counting to the number of databases, check the name of the database for each index and dismount that database
pseudo code would be
$dbstobedismounted = @()
foreach($cdb in $cdbs)
$dbstobedismounted + = $cdb.Name  //instead of actually dismounting
for(int i=0;i<$webapp.ContentDataBases.Count;i++)
$dabasename = $webapp.ContentDataBases[i].Name
foreach($dbtobedismounted in $dbstobedismounted)
if($databasename -eq $dbtobedismounted )
dismount-spcontentdatabase -dentty $webapp.ContentDataBases[i]
I'm sure you might have to do some modifications to make it work, but the point I'm making is instead of dismounting in the foreach loop, have a list and dismount in another for loop. Hope it helps.
rani