I'm not sure, if that was the case before. They all look perfectly smooth in the preview window.
Preferences / Miscellaneous / Advanced: [Image Formats] psd_image_preference
(Nothing has changed here for a long time, that I can remember. You might be noticing the PSD thumbnail resolution due to different scaling settings now, but the source image would've been the same before as now.)
The third option (the first one was the default) gives a clean preview. Thanks!