This particular problem is solved by my latest commit (r13295).
What caused it is the limit to the number of strings used in a WPS. A string is a piece of text written in the WPS that's not a tag, i.e. spaces, or things like "playing", "paused" and everything else. There can be no more than 128.
As of now, this is 128 unique strings. This means that if you use the exact same string twice, only one copy of it will be stored in memory instead of having it there twice.