Looks like we can't reproduce the issue or there's a problem in the test case provided.
Ext JS Premium Member
+1 for strict mode. I hope it was not a design decision to abuse the API and not being able to support strict mode at all.
23 May 2013, 10:43 AM
The Ext JS 4 class system relies on arguments.caller and we don't see any way to support strict while retaining our class coding convention. We don't plan to change the API in any significant breaking way within the 4.x line, so this isn't on deck for happening in that code line. We're taking a fresh look for future major releases, but after the breakage from 3.x to 4.x, we're becoming extremely sensitive about changing large parts of the Ext API surface all at once.
+1 on strict mode for the future.