Deleting from /tmp doesn't work

[Biscuit]

I have some images in /tmp
When I delete them in XnViewMP, it asks me whether I'm sure, I click "Yes", they disappear. However when I re-open that folder, there they are again. Confirmed in external file viewer that they're there.
Not a permissions issue - I run XnViewMP as myself, those files are owned by myself, and deleting them as myself from any other program works.
If I delete images in some folder other than /tmp, e.g. put them into ~/photos/and delete, then it works, so this bug is specific to /tmp
Version 0.72 x64 (Dec 19 2014)

[Biscuit]

Still valid in 0.78.

Put some images in /tmp
Run ./xnview.sh
Go to /tmp and delete them.
Reload folder or check with other program, they're still there.

[wwp]

Is /tmp a subdir of the root filesystem or a mounted drive?
Do you access /tmp from the Folders or the Favourites tabs?