scm-tags plugin leaves stale indexes on shutdown

The scm-tags-plugin is programmed to delete its cache entries when it shutdowns. However, stale entries has been observed in the Stash team's internal instance:

Bryan: stash-dev has ~30k cache files, and most of them are in scm-tags

node481:/opt/j2ee/domains/atlassian.com/stash-cluster/install/home/caches/scm-tags$ ls -lrt | head
total 75176
-rw-r--r-- 1 atlstash user     0 Nov 18 13:37 cache-entry5832135393360417073
-rw-r--r-- 1 atlstash user     0 Nov 18 13:37 cache-entry4191256713607527145
-rw-r--r-- 1 atlstash user     0 Nov 18 13:37 cache-entry9114455448116455716
-rw-r--r-- 1 atlstash user     0 Nov 18 13:37 cache-entry4878348930357163328
-rw-r--r-- 1 atlstash user   406 Nov 18 13:37 cache-entry4602207029660125443