I saw this issue as well. I upgraded from 7.9.somethingold to 8.1.28, and almost every single component with a font had its Dialog font replaced by that synthetica one, and it meant I could no longer save my windows if I made changes. I, as you said, had to simply edit the font and press OK. Note: my fonts in components still showed as Dialog, but if I probed them via script, I saw they were actually the synthetica object.
I ended up having to write a script to traverse all components on the page and convert them to the Dialog font, as there were far too many places to fix this in. Interestingly, if I dragged on a new component, it too was affected... I have a feeling this will affect development going forward. I should probably raise a support case