Aha! So WaveLab was the culprit!
Check the discussion about that here and also here
tl;dr: it is a poor way to detect non-realtime processing, it also leads to wrong detection in other hosts (SONAR is sure one of them) and should be avoided in my opinion.
If compatibility with WaveLab is an issue, then restricting that patch ONLY to WaveLab on Windows is a must, in order not to mess with other hosts that support the VST protocol way to report non-realtime processing properly
EDIT: also, adding a specific ‘if’ that checks the host to which the workaround applies, leaves a very useful trace in the code of the host for which the workaround is necessary. It is a nice thing to have when looking back at old code to understand why it was put there. (aside from, obviously, proper documentation with comments)