Getting 5% disk remaining with only 8 shows recorded?

For the life of me, I can't understand why I am getting this message when there are only 8 shows listed on My Playlist. At the most they total 8 hours, yet it is showing 4-6% disk remaining.

We have two R15 receivers that we use to record a large number of first-run shows each week then review later to see if client products have appeared in them. 

I did a reset both receivers this summer (refrag) and cleared everything, but the problem has come back on one of them, the disk fills... resulting is missing new recordings.

Am I missing something?