Odd mouse behaviour with FloatingPawnMovement

I’m attempting to create a floating camera. It seems to work fine just extending DefaultPawn, however there’s a circle in the centre of the screen where mouse rotation doesn’t work smoothly. Holding the right mouse button and moving the mouse in this circle won’t move the camera until you release the mouse button, then the camera will jump to a seemingly random rotation.

[Here’s a video of it happening.][1]

The only piece of blueprint code is this on the Level:

118126-levelbp.png

Interestingly, unchecking ‘Hide Cursor During Capture’ will cause it to work correctly, but you can only rotate the view until the cursor hits the side of the window.

This is happening on 4.14 and 4.14.1 on Linux.