Thanks for the report - the reason this is happening is because the "broken" themes are v0.7 themes, while the working themes are for MasterPlan v0.8. Did you simply unzip the newest zip file over your existing installation?
Viewing post in Changing Themes loads blank "Magenta" (windows)
Ah that makes sense.
I definitely do have my 0.7 and 0.8 unzipped into separate folders. I just deleted both and re-unzipped from scratch, and I notice all these extra themes are no longer in my 0.8 folder.
I must have accidentally combined them at some point, and just don't remember.
Anyway, if the theme format is so incompatible between 0.7 and 0.8, it would probably be a good idea to include some sort of version check in the theme .json files. It could be as simple as adding something like:
"Theme Version":0.8,
... at the top of the newer theme JSON files. That way if the selected theme is a lower version than the current Masterplan version compatibility, it would just display some message and not load the broken theme.