I also had a problem: it seems that qtip 1.x will not allow you to use a "radius" that is less than the width of the frame.
It looks like this is by design, and you have to upgrade to qtip 2 (which has not yet been released) to get around it.
qtip :
: , , , . , , , ( , ).
: , , , . 1.0 , 2.0 border-radius.