I can replicate the problem.
An alternative workaround to "both first runs and repeats" and deleting unwanted episodes would be to remove the series recording for now, and add single episodes as you want to record them. Then when you think you've caught up, add a "new episodes" series recording.
But what you're trying to do seems to be a reasonable thing to want, and perhaps there should be a way to do it if there isn't one now.
It used to work, I'm not sure when - ie whether it stopped working recently or maybe it worked with my previous pvr but doesn't work with the beyonwiz. It's taken me a while to realise there was a bug, for some time I just thought I'd got forgetful and thought I'd recorded an episode but must have forgotten to actually do it.
In terms of there should be a way to do it, the functionality to create the recording is there as "Schedule episode", it just doesn't work properly.
In terms of the suggested work around, that would be Ok for Who do you think you are at present as it isn't showing new episodes but would be problematic for Escape to the Country and other series that mix new and repeats where I don't want to have to manually add both the new episodes and older episodes that I may want to record.