I guess if you have never been out of status even when only on TPS, it says you are legal. I dont see a problem from that perspective. Lets say you have f1 and overlapping TPS, solo TPS, and now f1 then you should not be considered one who violated the status. For the sake of working on TPS while on F1, it looks like its a violation of F1 but I guess you can continue to be on f1 once TPS expires and you stop working. Otherwise whats doesn it mean by taking both parallaly?