another bug on T 51?

Substitutions only end when they are cancelled. Timing is done from when it is accepted and not how many hours it is used. The substitution system hasn't been reliable for quite a long time.

yes thats clear, the problem is, i gave one day sub and canceled it after 8 hours. so how are the other 15 days on substitution are coming? i dont understand that. if i give it and dont cancel it ok, but without giving to someone, why are the days are counting

Did the day you did this coincide with the timing of issues on Tib51?

thats possible, but cant say it concret