ObjStoreBrowser::probe uses System.currentTimeMillis to determine whether its list of allUids contains stale date during updateMBeans call.

Now if you imagine a clock which never moved on (low fidelity) then this would mean that a Uid was never eligible to be reaper from this list.

Or imagine a machine that is very fast (my laptop for example) and it is possible that probe, remove entry, probe can all be called in the same millisecond.