I was able to reproduced the jiggle both in Debian 12.x and CentOS 9 running your demo program with Java 23.0.2. In Debian the jiggle always happens. In CentOS the jiggle happens once or twice in a row, then a couple of times everything works ok, but then the jiggle comes back, and so on. I changed the visual effects setting and nothing changed. I removed the alert.initOwner() and nothing changed. Have you found a solution to this problem?