When I installed P-TBird, I neglected to disable "automatic updates". A week or so ago T-Bird 22.214.171.124 was auto installed on top of P-Tbird. This may or may not be related to my problem.
About the same time, everything left in my inbox from a previous session would be gone when I started the program. I searched Mozilla archives and discovered that this problem can happen if:
1. Too much mail is left in the inbox
2. Sub-directories of the inbox are created
One can test for this problem by doing a "Compact Files". I did so and all the missing messages re-appeared but were invisible again when I re-started. "Compact Files" would always bring them back.
I finally moved all "Pending" messages to a new folder in "Local Folders" and moved all non-standard folders to "Local Folders", did another "Compact Files" and I have had no problem since.
However my ex-wife, who I set up at the same time I did, is having the same problem but has no non-standard folders and keeps no messages in her inbox.
I'm not sure if the problem is T-bird itself, the Portable version of T-bird or the automatic update that Mozilla did to P-Tbird.
Any suggestions would be appreciated.