That was a very obvious effect of HF19, to such extent that the developers resorted to code hints in order limit this: one release of Condenser, the UI for Steemit, even unchecked the "Upvote post" checkbox which was, until then, checked by default. Some people were a bit baffled, until they realized they need to check that first, and everything returned to normal.
That was my pull request 😊 But I didn't observe that people just started checking again, have you anything to back this up or is it speculation?
I noticed that they started to upsteem themselves just as often... No numbers, though.
Didn't know it was your pull request, congrats or your contributions :)