Inconsistences in positioning & defining via kv language

[wbarroz]

Hi people!
First I must state it: I love this widget, but I find 2 problems:

1. I simply cannot position it using the pos_hint(x position relative to parent);
2. It behaves bad when set through the kv file
   I put the example attached when one can observe both problems. I use a .75 shift in the 'center_x' attribute, just to show the awkward behaviour, when compared to the expected(at least to me) knob behaviour.
   question.zip