I played around with it for a while, only the 306 [[MediaWiki:Senselessimagename/X|X]] links alone caused the error (in the preview) but on my test wiki with 1.17 I was able to paste the links 12 times and it did render fine (MW 1.17.0, PHP 5.3.1, memory_limit was 128MB, no extensions). I know that this isn't really comparable cause the extensions eat a lot of memory, but 12 times...

Ok, with some more testing I can now for sure say that it's a 1.18 bug. I've tried to submit just the 306 MediaWiki links on test.wikipedia.org but failed (with the interface and using the API) so by the time the bot on commons submitted the links it must have worked fine or it did the impossible ;)

Btw, I was able to paste the links 20 times on my test wiki now, without any problems

Possibly hitting all those links is hitting localization initialization: 306 languages is a lot of strings to load, and those are going to add up.

Yes, that's pretty likely the error always occurs in i18n files. But I still wonder how the bot could submit the page without an error...

I believe this has been fixed by r97815.

(In reply to comment #5)

I believe this has been fixed by r97815.

Deployed. Works now.