Is this a bug or a cache related effect? (Or both?)
Maybe it's only me?
Example: On the Related panel of this link there is currently a "Make it funner" related question that's no longer available.
It is possible for related questions to show a deleted question, as those lists are only rebuilt..
Interesting. In the example you give it is fairly recently deleted (yesterday), so it could be cache related; but that is pure conjecture...