I've seen lawyers at major, high-priced law firms make this same mistake. Once it was a huge list of individuals names and bank account balances. Fortunately I was able to intervene just before the uploaded documents were made public.
Folks around here blame incompetence, but I say the frequency of this kind of cock-up is crystal clear telemetry telling you the software tools suck.
If the software is going to leverage the familiarity of using a blackout marker to give you a simple mechanism to redact text, it should honour that analogy and work the way any regular user would expect, by killing off the underlying text you're obscuring, and any other correponding, hidden bits. Or it should surface those hidden bits so you can see what could come back to bite you later. E.g. It wouldn't be hard to make the redact tool simultaneously act as a highlighter that temporarily turns proximate text in the OCR layer a vibrant yellow as you use it.