Perhaps there is an explanation for this - but as far as I can see this is a bit of a bug.

When you resolve an issue, why would it be assigned to the person who resolved it?

I suggest that the fix that makes most sense is that the the label changes from "Assignee" to "Resolver" (it seems that all the rest - filtering in reports etc all works fine).

I would also suggest that on re-opening an issue the assignee should be treated in much the same way as when creating an issue (either it goes back to the lead developer - or the user gets to choose (and one of the choices is the "last assignee before it was closed").

-Nick