Trying to figure out this weird situation (and crashes)

I have a tab control, 3 tabs, and listboxes in two if them (hierachial data), and I enable/disable tabs based on if the listbox has a selection or not. I also made a small proof script for this to show what I mean.

Now, the real script does a lot more than just enable/disable the tabs, but the weird thing is I get this error:

Script Error: Line 512

<span style="color:rgb(255, 0, 0)">Error: cannot access member `valueOf&#39; of deleted QObject</span>

<span style="color:rgb(255, 0, 0)">Stack Trace: ()@/Volumes/DuoDisk/DAZBoot/devContent/Scripts/Roll Em Up.dsa:512</span>

After  a few steps around, in this code:

this.wTabControl.setTabEnabled(this.wSectionGroupBox, true);

So, it looks like for some reason the members of the overlaying class for some reason gets deleted, the offending object is this.wSectionGroupBox as when I try to debug() it I get the same error.

What makes this difficult is that DS crashes rather frequently or (the error is shown, but even debugger while stepping just shoots DS down, so I get flashbacks from the old Mac OS 7 development cycle (edit-test-crash-reboot)

Any ideas? What I do "besides activating tabs" is manipulating viewport scene elements, but that doesn't crash as long as I refrain from activating/deactivating tabs.