Hey Toril,
Make sure the style volume slider isn't too high in relation to the R1,R2,R3 volume levels. Also make sure that Initial Touch sensitivity isn't set too high as you would need to strike the keys much harder in order to hear the sounds that you play, maybe set the sensitivity on Soft 1 or any one of the others that you feel more comfortable for your playing. I'm very certain it's not due to a faulty keyboard.
And I can also agree with you and the others that find that some of the OTS levels are very inconsistent throughout the different styles. I do not use them on a regular basis, but in the rare occasions that I've had, I also notice that. From in my experience, the faster way to balance it is reaching for the Style Volume slider and adjust it accordingly to the particular need.
Cheers.
Valentin