Switching from class to class sometimes is slow

On the memory diff tab, after taking a snapshot, pretend we have classes A and B.

Selecting class A performs computation to calculate the set of retaining paths for to A. Then selecting class B, does the same thing for all the retaining paths of class B. Selecting class A again should be fast, since we have already performed this work. But it appears to take equally as long to compute the set of retaining paths. I suspect we are not caching this computation.