Strange, platform specific Pango crash

This problem spans so many components that I don’t even know where to file a bug report, so I am asking here. I encounter two strange crashes originating from Pango while investigating this issue:

The setup is Pop OS 21.04, and the crash happens with a combination of IBus Chinese (or Korean, Vietnamese, according to reports) + Pop Shell Launcher + Gnome. I have determined that the Pop Shell extension has nothing to do with the crash, but it does provide the input textfield that allows the crash to happen.

The first crash happens as an assertion failure happening in itemize_state_process_run(pango-context.c:1441), called from a loop inside pango_itemize_with_base_dir(pango-context.c:1582):

assertion failed: (state->run_end != state->run_start)

I do not know if this is a Pango bug, but given that this is an “internal” assertion failure, it might very well be.

The second crash seem to be a memory access error, originating from pango_font_description_copy(fonts.c:809). If I at least had an idea about where the first crash came from, I have no idea about this one because I could not get GDB attached to Gnome shell at all.

I can’t attach the stack trace here, because it is too long.