Created attachment 6939 
gdb stacktrace

(Thunar 1.6.10git-45fb3a15)

An assertion failure (stack trace attached) can be triggered reliably by navigating thunar to a folder containing the script 'exercise.py' and running that script (which randomly creates and renames files to check whether file system events are handled correctly).

Error analysis (thunar-folder.c):

1) thunar_folder_reload starts a new job and returns

2) thunar_folder_content_type_loader is called from a different context and sets content_type_idle_id

3) thunar_folder_finished is called when the job finishes and causes the failure because content_type_idle_id != 0

Goodie:

I will also attach a stack trace for step 2 in case this helps (obtained by adding a check for folder->job == NULL in thunar_folder_content_type_loader).

It's certainly easy to provide workarounds but I don't understand the logic well enough to provide a proper fix.

Cheers,

Christoph