My parents had Men in trees record even though it was a rerun.
I have had my HR20 less than a week, but I found the following "quirk" when setting up my Series links:
1. Selected desired program in guide (in this case a repeat).
2. Hit the Record button twice to set up series link
3. Went to Series link tab to verify it is set to First Run only (previously done through preferences)
In this sequence, the initial show was a rerun, but it still showed up in the to do list. I suspect the fact that I started the recording sequence through that episode forced it to record even though all future episodes seemed to setup correctly.
I just manually deleted the initial repeat.