Problem with Address Line 2 in Contacts

Question

I am currently syncing my contacts with my Yahoo mail.  The problem that I am having is that we live in an area where most people have an Address Line 2 (Usually their PO Box).  I am able to enter their PO Box into the Address Line 2 field in contacts.
This is the problem.  After about a week or so the Address Line 2 will attach to Address Line 1.
Example:
Line1: 123 Main St.
Line2: PO Box 456
After a week it turns to...
Line 1: 123 Main St. PO Box 456
Line 2: (blank)
Thanks,

Answer 1

magovoru - your reply is confusing!
if I take a backup and later restore it - the backup should give me same data as it was on the phone. It simply does not make sense to remove certain things (phone number label) because only a couple of phone support this.
If you mean that the functionality to edit the label will not be available - well let it be. But at least restoring the backup should be as it is otherwise it only increases problem.
AND for your information - this 'only couple of models have this feature' thing is one feature which I use regulary