Moving files to the trash seems to be the default in newer pcmanfm. As long as "real" deleting is not enabled, the menu should not say "delete" but "Move to Trash" and it should certainly not use the delete icon in that case.
This issue should be handled in 1.2.0-beta0 version of libfm. Test it, please, when it's possible for you. Note that you should recompile pcmanfm as well to use new version of libfm.
Thank you very much.