Currently, right after removing a person (which i.e. removes it from personIndex), we call personChanged.
Which itself tries to access personIndex with recently removed key, which creates a default (invalid) value with such key.
In the end we obtain inconsistent (invalid) index, which leads to crash.

I've noted the bug when was working on T9595: [KAddressbook] Use KPeople model for contact list, see scratch repo and "testab" application there.
It's sufficient to check/uncheck address books several times to crash it.
After applying this patch, it no longer crashes.