Thank you for reporting this bug. We will make it our priority to review this report.
Ext JS Premium Member
ExtJs 4.2.3 Performance issue on border layout : too many useless layouts
When the border layout have a collapse zone, floating it out generates several useless layouts of untouch zones.
Here is a fiddle with a border layout. Open the console to see the "layout" events.
When floating temporarily the west zone (by clicking the bar - not the button), I would expect to have only "west layout" in my console, but I can see this
which means that the opened zone is layouted once (normal) but all other zones are layouted twice (they should not be layouted at all).
north layoutwest layout
I have a big complex UI in my app, so each time a collapsed zone is temporarilly displayed, all zones are uselessly re-layouted.
We have some ideas in general about preventing extraneous layouts from running however it's a difficult problem to solve in a generic fashion. Depending on the scope of the changes required we may back port that kind of improvement to 4, however we'll need to evaluate it once it comes in place to the codebase.
Twitter - @evantrimboli