Trash is not supported on AFP mounted shares. The symptom you see is therefore likely a side effect of this. (c)
As for me It's benediction. Developers often provide buggy updates of thier apps or perhaps you have obsolete apple iOS device (like iPhone 2G, 3G etc., or iPad of the first generation) — in Previous Mobile Applcation folder you can always find previous ver of the app and install it instead of buggy one or unsupported by your device.
After all you can purge this folder from time to time or even delete it (but it's gonna be created again during the next update).
Yep, you're safe to delete this folder.