Have you tried if the problem goes away when you reorganize NOW?
I've never seen this problem of Trados not adding segments to the TM as described by you, BUT I've had cases where the segments were in fact there - they just didn't appear in matches and concordance searches if the database was in urgent need of reorganizing.
Thank you very much for helping - I will try that. If I will not write anything soon, it means the problem is gone.
Have a nice day,