Default [Q] Compass in Landscape orientation

Using 4.4.2 CM11 nightlies, Philz Touch

My compass acts oddly when my phone is in landscape orientation. It works fine in portrait orientation. If my phone is flat on a table (i.e., the screen is facing directly up), it's fine. As I rotate the phone vertically (with the power button facing away from me), it works up until the phone is about at a 45 angle from horizontal. Then the compass can sweep though an angle of about 180. I see this behavior in GPS Status & Tools and with the blue arrow in Google Maps.

In portrait, everything is fine. I prefer to have my phone mounted in landscape when I'm in the car. This is when I need my directions to be correct, and this is precisely when they are not.

It seems that there's nothing telling the compass that the phone is in landscape orientation. I don't know if this is a hardware problem or an issue with CM11.

However, Google Sky works when the phone is in EITHER orientation. I have no way to explain that.

I cannot find anything or anybody else describing the same issue or any way to resolve it.