Activated sleep timer turns itself off after a full charge

[lubatur]

The activated sleep timer turns itself off after a full charge, traceable on my FiiO m3k and Surfans F20.
I can't find a way to disable this in the settings or manuals.
Installed are the native ports with actual development builds.

Thanks for your help.

[lubatur]

Could someone please check?
I think this is a general problem, or is it intentional like that?
Can it be changed?

[lubatur]

I solved the problem by reinstalling rockbox.