Highlighting becomes cloudy

I have been highlighting scanned pdfs for the past several months now with no issues at all. However, recently adobe has been changing my highlight tool to also affect the text rather than the background. I don't know how to resolve this issue, and I need some help!

The top highlight is what my tool previously looked like and the bottom highlight is what it is doing now. I have tinkered around with my preferences to fix this, but I am at a loss.