I have come across a syntax tree with a subordinate clause phrase (as opposed to just a sentence) whose left daughter is a verb in the imperative, e.g. Wash your laundry tonight.
Last, I also searched several thousand parsed trees but not a single left daughter was a verb to the subordinate clause phrase.
My conclusion is that it's a tagger mistake.
Edit: Here is the utterance for context
Review your homework for 30 minutes and make sure it is complete.
In the tree, review is assigned the part-of-speech label for a subordinating conjunction, being the left daughter to that subordinating clause.