Sequences can't be merged if user doesn't have enough permissions to save the result file

Open several sequences simultaneously. A "Multiple Sequence Reading Mode" dialog is shown.
There are two merge modes (into one sequence and into a msa) that suppose saving a new document. If user doesn't have enough permission to save the result file, then save task will fall and sequences won't be merged at all.
There shouldn't be a possibility to accept the dialog if the result file can't be saved OR a new document should be successfully created, even it wasn't saved.