I placed this control in a test app, and it works fine. But in my business app, which has a Silverlight 4 implicit theme applied (AccentColor theme), the up/down buttons are too wide and non-functional. I know for sure this is not what the theme calls for - I found a site showing off the theme on various controls, and the NumericUpDown control looks normal and is functional in every way:
http://www.silverlight.net/content/samples/sl4/themes/accent.html#/Toolkit
I've also placed this NumericUpDown control in various areas within my app. Still same thing. I've also tried to apply an explicit style of targettype NumericUpDown (the style being an empty style). But still the same thing.
Anybody seen something like?