Please click the toolbar button 2 times in succession. You will notice that the document gets masked (for no apparent reason).
To me, the problem looks like with the dots in xtype for the custom component: Ext.ux.CustomSheet
Okay so, I tried to remove the dots replacing them with an underscore. Guess what, a js error is triggered as soon as I click the toolbar button.
If I eliminate both underscores as well as dots from xtype, I still get js error on clicking the button.
Dots are not valid characters for xtypes in Touch 2, underscores (or dashes) are perfectly fine. I can't re-produce the issue you described with PR3 build when changing your xtype to either "ext_ux_customsheet" or "ext-ux-customsheet".