It could be a wikidata bug. "If an entry is posted via API and error occurs due to the interwiki conflict, new entry is not created. But new entry number is consumed and NEVER used again". These gap can be found other bot editings.
It's true that IDs may be "swallowed" by unsuccessful attempts to create an item. But I don't see this as a problem. The IDs have no significance, they could just as well be chosen randomly instead of sequentially. The ID system may well be changed to something else entirely at some point, e.g. GUIDs.
I want to thank you for reporting this anyway, because it *might* have been an indication for Something Bad happening, like items just vanishing without a trace. But I don't see any evidence of that. So, closing WONTFIX.
(In reply to comment #4)
From what I've heard, it's enough to visit Special:NewItem to "consume" an
True, the only damage is that it hurts our milestones addiction. :)
That's not correct. But any attempt to create an entity will consume an ID, including failed attempts.
(In reply to comment #5)
That's not correct.
Ok, let me rephrase that: if that was true, it would really be a bug, and one that should be fixed. But before filing a bug report, please make very sure that IDs are actually being consumed without any attempt to create anything.