If you look up a DiscID which matches multiple releases and press enter (or presumably any non-numeric character), you will get this nice little exception:
Traceback (most recent call last):
File "/usr/bin/isrcsubmit.py", line 620, in <module>
releaseId = disc.release.getId() # implicitly fetches release
File "/usr/bin/isrcsubmit.py", line 348, in release
self._release = self.getRelease(self._submit)
File "/usr/bin/isrcsubmit.py", line 382, in getRelease
self._release = results[int(num)].getRelease()
ValueError: invalid literal for int() with base 10: ''