Thoughts about this fix:

I do wonder if this (firmware change) is the best way to fix this problem.  The fix doesn't seem to be needed for at least some versions of DJI/Naza GPS clone, so some testing needs to be done to see if it hurts those versions.  Or we could put a switch in the UAVO to turn it on/off.  There doesn't seem to be a way to detect whether the GPS is authentic or clone.

Also, it would seem that this is a simple delay that could be fixed by adjusting some PID, yet I haven't been very successful adjusting VTOLPF horizontal PIDs in place of using this code fix.  Maybe there is even an interaction between horizontal and vertical PIDs.

Also, it is possible that this GPS has an issue such that when you just tilt it, it reports a different location even though you didn't move it horizontally.  This seems unlikely though because you can recreate the issue or a similar one with a Ublox GPS set to Pedestrian.  Also, I forget whether the Ublox recreation is just east west.  I suspect it is not, and thus may not be the same issue.

I remember doing experiments to mount a GPS higher to make sure it is not a local electro-magnetic field affect where the extra field causes a request for attitude change that makes that motor work harder that makes the field stronger... and finally reverses making the field change weaker and weaker as the motor is slower and slower.  This needs to be recreated/retested.

Conceptually there is an issue where tilting east west affects causes less mag field change than tilting north south.  Imagine rotating around the mag field vector where there is zero change.  This may require a change to the EKF to have a different correlation for north south tilting than for east west.  Do we have any users that are close to the Earth's equator?  This problem might be really bad for them because their mag vector is horizontal.

Also, one user (Tongala) reports that for him, the problem did not happen in RC2, but did happen in RELEASE.  Is it this simple to find the issue, or is it a tuning issue that randomly happened to this tune (his release tune) but not to that tune (his rc2 tune).