Hi Klaus,
Yes, thinBasic is based on PowerBasic but due to licence restrictions of PowerBasic in developing compilers or interpreters using PowerBasic, I cannot wrap 1 to 1 PowerBasic functionality.
For this reason most of thinBasic functions are a high level rewrite of the one you can find into PowerBasic.
In this case Extract$ is my own function and not PB wrap.
thinBasic Extract$ does not support negative start position (check in help about that) but I will be happy to try to add it.
I've moved your bug request into feature request area.
Remain$ is another function where I've developed in thinBasic a complete new function instead of wrapping PB one
Ciao
Eros