@Michael, could be the case that your checkbox does not refer to the correct callback! Try to edit your GUI with GUIDE (beware of not changing anything of the figure editor!) and check the Objectbrowser. There you see the callback your checkbox refers to!
I experianced some major issues using tabPanel:
When testing the gui, fast switching between tabs restarts my gui..
When using tabpanel, no object attributes can be changed anymore after closing tabPanel (workaround: Objectbrowser with GUIDE on gui.m)
Do not try to add global tools to one of your tabpanels - will result in complete loss of your figure after saving!
I like this programme, although it still has some issues which can be very frustrating... (spent hours of redundant work caused by loss of elements and wrong callbacks / createfcns)