`-p` and eventlog produces an invalid eventlog

I am trying to use the cost centre profiling support in the eventlog with 8.10 but it seems that when there are multiple threads that specifying -p -l can produce a corrupted eventlog.

When you try to decode it using ghc-events you get failures such as ghc-events: Ix{Int}.index: Index (768) out of range ((0,207)).

At the moment I don't have any further information about why this happens or how to reproduce it with a small case.