The bug in 7650 getHeight() has definitely been a FAQ on this forum and no one has been able to suggest any solution to it.
Since I'm not Nokia, I cannot fix the problem but I have a workaround and some more info:
I noticed that the bug manifests it self when called from a Canvas that is not the first Displayable set to the Display.
For example, previously I had in my application a "splash" screen that was displayed before the actual application Canvas. That screen extended a Form. When that screen exited, the actual application screen was set to the Display.
The Canvas got the wrong getHeight no matter when the getHeight was called (in constructor/after constructor, after/before adding commands, after/before first paint request, etc).
But then I removed the "spash" screen and put the application Canvas as the first Displayable set to the Display and everything started working fine.
The lesson: get to the point, and leave the spash screen out. ;-)
BTW: How the h*** do I report bugs to Nokia. They only thing they seem to have is "issues" that cost me. I do not want to pay Nokia anything for doing their test work and reporting what I would say is a quite good and elaborated bug report.