Over the years that I've trained writing teachers and taught students who've been the victims of grammatical mis-education, I've become rather jaundiced about the quality of grammatical analysis that you see in the public sphere. This morning, though I ran across a version of this mistake that raised my eyebrows. It's exactly parallel to the ones that Pullum identifies, so it's not the error itself that's unusual but the people making it.
On page 67 of a paper called "The Linguistics of Readability," written by two computational linguists, is the following:
Consider these two sentences:
1. “We endeavor to maintain the spinning of all the plates.”
2. “We try to keep all the plates spinning.”
The first sentence uses passive voice, the second uses active voice.
Uhm, no. Both sentences are active. The first sentence uses the polysyllabic words endeavor and maintain and turns spinning into a noun, all of which decrease the sentence's readability, but voice has nothing to do with it. Apparently it's not just educated laypeople who can't identify the passive. Even some computational linguists have problems, although to be fair I suspect that they are more on the computer science side of things than the linguistic side.