set rest pose issue with arm position

I'm working on a character with arm tracking movement.  All seems to work fine, all the rigging is done correctly (I presume...)  and dragging the arms manually with the mouse seems to be working fine.  When I try to set the rest pose (standing in an 'A-shape' with my arms straight), the character's arms lift up and bend in a sort of 'hands on hips'-position with the elbows in a 90 degrees angle.  The arm tracking now works well, but it's impossible to let the arms hang in a basic position without the elbows bend.   I've tried already to manipulate so many parameters without results yet. Any idea what could be the issue?

Thanks!