It should probably go without saying that you don't want your publishing contract to include clauses that contradict one another.
Beyond any potential legal implications, internal contradictions suggest a publisher that either doesn't understand its own contract language well enough to spot the problem--or a publisher that simply doesn't care. Neither is a good sign for what lies ahead.
Contradictions can be tricky to spot, especially for first-time authors who aren't experienced in contract legalese. Here's an example that came across my desk recently: an anthology contract from Dark Lake Publishing that provides for rights reversion 12 months after publication:






