In case anyone has this same issue (like I did) here's what I did to "fix" it:
Border layout, 3 regions (west, center, south) that were subclasses of panels, collapse buttons disappearing on collapse.
I "fixed" the disappearing collapse buttons by taking the config option out of the subclasses. So, the items of my panel that had layout: 'border' looked like this:
instead of specifying collapsible: true within each subclass. It also works to use the defaults config option.
xtype: 'detailedview' //my subclass
xtype: 'applicantview' //my subclass
xtype: 'sidePanel' //my subclass
Hope this helps someone...
By the way I don't know why this works and maybe someone with a bit more knowledge could shed some light :-)