Regression in 21.0.8 from 8348989: Better Glyph drawing?

[Mikael Sterner]

I see a regression between OpenJDK builds of 21.0.7 and 21.0.8 in
rendering of glyphs on macOS, that I think is due to commit 10a28c0
for "8348989: Better Glyph drawing". A bisect between tags
21.0.7-ga and 21.0.8-ga indicated this commit as the first bad
commit, and reverting 10a28c0 and the followup 2801e11 in
jdk21u-dev/master also removed the problem.

Repeat:
1. Modify HelloWorldSwing.java[1] to show the string
   "aBCc\u7b80AaBbCc" instead of "Hello World!"
2. Run it with java HelloWorldSwing.java

Expected: Label showing "aBCc简AaBbCc"
Bad result: Label showing "aBCc简 aB Cc" (missing A and b)

OS: macOS Tahoe 26.2
Hardware: Mac mini, Apple M4 Pro

It seems like only glyphs that have already been rendered before
rendering the CJK character are visible after it, any new glyphs
are blank.

Interestingly the issue cannot be reproduced with 21.0.10+8-LTS-217
from Oracle, but I could reproduce it with e.g. Azul Zulu
21.0.10+7-LTS. It is also not there in Azul Zulu 25.0.2+10-LTS.

Yours,
Mikael Sterner

[1]
https://docs.oracle.com/javase/tutorial/uiswing/examples/start/HelloWorldSwingProject/src/start/HelloWorldSwing.java