[RunnerFL]

Because my son NEVER deletes anything and I don't want 50 episodes of Phineas and Ferb in HD taking up all of the space on my HR24. SD will take up a lot less space.

You could just create a Series Link on the HR24 to record Phineas & Ferb in SD for him.

The only guess I would have as to why the HR24 wants to record the HD version is because it's an HDDVR and when a channel number is selected it defaults to the HD version. When it gets the request from the H21 to record what's on 292 it selects the first 292 it finds, the HD one.

Another option would be to put an external 2TB drive on the HR24 and not worry about space.