Thanks for your Tipps!
> Since it is repeatable in your machine, you can compile a new postgres
> version with "--enable-cassert" (enable assertions in code) and
> "--enable-debug" (enable gcc debug support) configuration. Then run it on
> your data and "bt" the core dump.
I try to found out the reason for that behavoir.
For now i could drop this damaged table und restore it from an older
backup, so all works fine again.
regards,
thomas!