I'm catching hell on this. At first, I thought it was a Windows / Mac issue, but you and I are holding out, at Windows 8.1. So I just updated H9 Control 2.6.0 (for the SpaceTime algo), and went back through the preset list process repeatedly. Dragging & dropping (or Importing) my own .h9z files kept returning "contains no presets or presets list" errors. This after renaming, re-saving, etc. Then I started rebuilding the same preset lists from scratch, using the original user presets.
But you provided a key clue. The presets list file size kept increasing with every action; each one adding the original file size to the new total. I got up to around 153-175K for 30 presets, in a size-limited list. Obviously, something's wrong here. It's as if a 'blank' list gets appended onto each rename, save-over, or re-export action.
I have been trying to reproduce this issue, but so far I haven't been able to. I tried using H9 Control on a Windows 8 machine, but I didn't see the problem occur there. It was a 32 bit Windows installation though, and you are working on a 64 bit Windows 8 installation. So, I'm guessing it may have something to do with your OS being 64 bit. It's on my todo list to set-up a 64 bit Windows vm and try to reproduce this problem in that environment.