While testing JDK-8232589, I noticed following issue with was reproduced with JavaFX 8u231 and OpenJFX 14, so I think this issues exists long time ago.

Force media player to use OSXPlatform only by specifying -Djfxmedia.platforms=OSXPlatform

Run application FXMediaPlayer (can be provided by request), open any media file (mp3 will work) and hit play. After that adjust rate to something different from 1.0 and pause playback. After playback is resume with play, rate will be reset to default 1.0.