Dragging QListWidgetItems with icons makes program crash under some desktop envs, not others

I noticed a crash in a program I develop, when dragging certain items (the ones that have an icon) from a QListWidget to another, when running under Plasma Desktop or LXQt, but not on Xfce or Mate.

I made a very small proof of concept, here: https://gitlab.com/bugpocs/WidgetListCrash

(I'll make an attachment if that helps)

The crash looks like this, triggered after dragging one of the items with icon from the left-side list to the right-side list:

 ./WidgetListCrash 
 Trying to construct an instance of an invalid type, type id: 6553705
 Trying to construct an instance of an invalid type, type id: 788558336
 Trying to construct an instance of an invalid type, type id: 524358
 terminate called after throwing an instance of 'std::bad_alloc'
 what(): std::bad_alloc
 Aborted (core dumped)

(I'm attaching a backtrace)

Dragging the items with no icon works fine.

I've tested this under Mageia, Debian and Archlinux, some i386, some x86_64, some under Plasma, some under other environments.

The crash does NOT happen under Xfce or Mate, for instance.
The crash also doesn't happen under Plasma, IF I run the program with XDG_CURRENT_DESKTOP=something-other-than-KDE. Besides Plasma, the crash also happens under LXQt, unless doing the above trick.

So basically, it seems like the crash is averted when Qt believes the environment is GTK-based.

I can reproduce this consistently, every time, under Plasma 5.10.4 or LXQt 0.11.

I found this other bug which looks very similar: QTBUG-15265

...but that one is a more complex case, and for Qt 4. Ironically, my crash doesn't happen when building the example with Qt 4, only with Qt 5.

Thank you for your time!!