Thanks for your positive comments about our modules.
How often does this issue happens? Does it happen only to some specific customers?
Usually the address should be replaced by the real post back from Paypal, there must be something happened for those customer, maybe something related to other 3rd party modules such as 2checkout like you said.
If you are able to find a way (steps) to reproduce the issue, we may be able to find our the cause and help fix that.