Success! Looks like we've fixed this one. According to our records the fix was applied for
a bug in our system
a recent build.
Piechart Bug: Slices become white after clicking on Legend
As seen in this demo:
When I click values in the legend to prevent them from displaying, the pie area associated with the bottom most value in the legend becomes white. You have to mouse over the said pie area to turn it white. After turning white, it permanently becomes white. The only way to prevent this white behavior is to only successively click on the bottom most value in the legend. This will result in no areas turning white but makes clicking on the legend to restrict the data set useless.
Sencha - GXT Dev Team
Thanks for the detailed description. This bug was introduced in beta 2 and has been fixed for the next release.