Well if he had the complete staff due to him having more complete portions of all the tailed beasts, then it would make sense that his staff revert to some lesser form, seeing as he lost parts of two different tailed beasts
**Edit** I was saying this to say that I thought he did this on purpose and this was supposed to happen since it's the same staff Obito had (always wondered why the incomplete Juubi jin had a complete staff) but then he went back to the other one so I think the entire thing is backwards period