Keep at Most setting

The setting "Keep at Most" under Record Defaults does not always work as expected.  If I set "Keep at Most" to 5 then only 5 recordings are kept and the oldest one(s) over 5 are deleted.  If I set "Keep at Most" to 10 then nothing is ever deleted.  I have counts of 11 and 12 in a single folder.  This is happening on two different DVRs of the same model.  Does anybody have a solution?