Play Panel issues

Hi!
I'm using Musescore V1.3 on a Mac OS X 10.7.5 machine, and somehow I find no way to adjust
the controls of the Play Panel accurately.
As soon as I change the "Tmp" slider to another value than 100%, it's somehow impossible to
set it back to 100% - either it drops to 99% or to 101%.
There are obviously some sort of value gaps, you can't adjust to.

What can I do to get back to exact 100%?

All the best,
Christian