which causes the panel to be disabled somehow (the title disappears and the collapse button disappears), after which the panel can no longer be expanded or collapsed.
el is null
out = (v = el.style[prop]) ? v :
ext-all-debug.js, line 8216
but this does not lead to the panel being practically disabled as in IE9 so in FF8 I can still continue to expand and collapse.
Even after making the panel empty (because I thought the child components that were causing it), I experience the same thing. It takes about 2-10 expand/collapse sequence to duplicate it. It is a lot easier (a lot fewer clicks) to duplicate in IE than in FF.
This is how the panel is created (this, even, has been simplified to make sure it is not a config issue):
When I posted it first, I didn't think of doing it on a clean example. Sorry. When I did I could not reproduce it. So I'm just confirming what you all have said.
There must be something else in our application that is causing it. I see the behavior I reported in multiple panels (even on an empty one) and it is really triggered by the collapse and expansion of the panels.
If I figure out what it is I might just post it here for the record (whether it is a bug or not).