Offline problem - deletes content of sync folders

Hi all,
using Portable TB version 1.5.0.5 (20060719) - installed as Portable but with automatic updates (if any) on my Flash device

I have twi IMAP accounts set up for OffLine sync and when I
1) hit File -> Offline -> Work Offline to sync
2) correctly remove Flash and move it to my home Laptop with no internet connection at all
3) run TB for the first time

it actually runs well

BUT when I close down TB and try to run it next time all content of my IMAP accounts is gone and I can see only inbox.

even I can see I have some content in IMAP folder on my flash, i cannot see it from TB

when I move my flash back to Pc hooked up to the net and go ON LINE entire content of IMAP accounts gets freshly downloaded. There is no damage to my accounts, exept I cannot work Offline (at home) with my email which is wery unpleasant.

I can reproduce this behaviour anytime.

I'm desperate, thanks for your help
Michal