Inexact cache key match

Was rolling out a new set of dockerfiles that were incompatible with caches from earlier CI jobs. On the branch with the new dockerfiles, I appended -v2 to all the cache keys in my CircleCi config. This prevented the new branch from trying to use an incompatible old cache, but the surprise was that other branches with the old dockerfiles/config (no -v2 in cache keys) started matching, loading, and choking on caches created by the new branch! Seems that, some how, the appended -v2 was ignored when matching on the cache key.

Screen shots and links:
New branch with -v2 cache keys, running as build 32848, saving cache with key top-level-dependencies-2UvLC_bLutn8MPZlWngM2b2WcSg0N1hWMRaskhr8HTo=-v2

Old branch with non-v2 cache keys, Found a cache from build 32848 at top-level-dependencies-2UvLC_bLutn8MPZlWngM2b2WcSg0N1hWMRaskhr8HTo=. Appears to have made an inexact match, ignoring the appended -v2!
(oops, limited to one media upload, but this one is easy enough to see by following the link)