1.  Are you using any custom themes?  If using one of the default theme 'Platinum' for example, does the same behavior occur?

2.  Does the behavior persists after an IISRESET?

3.  Does clearing the browser's cache change the behavior?

4.  You can try clearing the control cache by appending 'CacheControl.ashx?m=CLEAR' to the Designer/Runtime URL and browsing to it and retesting the control afterwards. I.e.:

https://k2.denallix.com/designer/CacheControl.ashx?m=CLEAR
https://k2.denallix.com/runtime/CacheControl.ashx?m=CLEAR

5.  Are other controls affected or only the Picker control?  Is the Picker control affected on all forms or only certain forms?