Don't treat every partition that can be unmounted as "removable media".

[Adityashaw]

Almost every partition (other than root and home) can be unmounted and they're treated as removable media.

Why is this a problem?

If I check the option Preferences -> Behaviour -> Erase files on removable media instead of "trash can" creation then I am unable to use trash even on my HDD and SSD partitions which are essentially on the same disk as my root and home partitions.

Possible solution

Change this line : https://github.com/lxde/libfm/blob/master/src/job/fm-file-ops-job-delete.c#L351 to something that can detect the underlying disk as removable or not... I don't know if it is possible or not... Thanks! Please ask if additional information is needed.