OK - there is a new version (1.6r0) out there now that corrects one issue and provides some more information and control to help you fix some of what else appears to be going on with your system. Please upgrade to the new firmware as well as the new setup client.
First, the angle velocity mode issue.
This was a bug in the software - it is now corrected. The angle velocity feature worked properly as one of the modes if you were using the "mode select" switch feature - however (as you saw) it wasn't working when you selected to always use that mode for a servo channel. In the latest version, this is corrected.
Regarding the pawn problems that you are experiencing. There appear to be a couple things going on here. Let's look at the drifting to left first.
Is this happening when you are in heading lock (switch in mode 1 or 2) or when you have heading lock disabled (switch in mode 0)?
If it is happening with heading lock disabled (mode 0), then it has nothing to do with using or not using the magnetometer. In this case, what I would suspect is that either the servo center position is not correct or the yaw stick from your radio is not sitting at the same value when it returns to center. These are the only two things that can effect the yaw servo in this mode. I know you said the servo center position was correct - so perhaps it is the transmitter stick.
When the gimbal board starts up, it looks at your stick positions and assumes that they are centered. Whatever value it gets at startup it will use as the center value - so make sure your radio is on before starting the gimbal and the sticks are centered. Then the firmware has a deadband range around this center where it will ignore small amounts of motion. This is to account for the mechanical slop that is present in transmitters. It is possible that this deadband range is not wide enough for your transmitter. In the new version (1.6r0), we have added the deadband width as a user-configurable parameter. You can find it on the Receiver Config page. There is a button marked "Set Bands" for each receiver channel. In addition to the deadband, you can also set the ranges at which it considers a switch to be in position 0, 1, or 2. You don't have to set the switch band values for a channel that you are using as a stick, or vice-versa.
If the drift is happening when heading lock is enabled, there are two possibilities as well. Again, the problem could be the yaw stick. In heading lock mode, the yaw stick works a bit differently. Instead of just sending a pulse width directly to the servo, it actually moves the heading value which the gimbal is trying to lock onto. This value is now displayed on the main screen of the gimbal configuration utility, labeled "Heading Lock". If you set up the gimbal and it begins to drift in heading lock mode, have a look at the "Heading Lock" value. If it is drifting, then the yaw stick must be sending a value that is outside the deadband range and causing the lock position to move.
If the heading lock value is not changing and it is drifting, look at the heading value. Is this value changing at all? It should not be moving very far away from the heading lock value. If you are seeing drift, and this value is not moving away from the heading lock value, then there must be a problem with the heading estimate. The most likely cause of this is temperature based drift on the gyro. If you are seeing this, repeat the gyro temperature compensation procedure and try again.
