Summary says it all. Reproduced on 2014 27" Retina iMac and 2017 MacBook Pro. Let me know if you need anything. macOS 10.15.5 Safari Technology Preview 109
I believe this was fixed in r263112 (bug 213224).
Definitely looks like the same bug. If I am reading that correctly, it looks like the fix was committed on June 16th? Is there a way to confirm it made it into STP 109 in Catalina?
Looks like STP 109 is based on r263346, so this may be a different issue.
Sorry - looked in the wrong place. STP 109 is based on r263074, so it doesn't include the fix. *** This bug has been marked as a duplicate of bug 213224 ***