Deploy Direction briefly changes when control-surface crosses CoM
Whenever the actuation axis of a deployed control surface crosses the center of mass of the craft,
the direction of deployment quickly reverses, then returns to its correct direction at normal actuation speed.
In the base game, we can most easily move the CoM by pumping fuel. The deployed winglet glitches when the pumped or moves the center of mass across its actuation axis. (If we un-deploy the winglet and use it for yaw, the direction of yaw control correctly reverses when the CoM moves across the actuation axis. The deploy direction, however, is not supposed to reverse, and does not reverse in the long-term, except for a momentary glitch with takes a second or two to recover.)
This rarely causes problems in the base game, but with Breaking Ground, the control surface can easily be moved so that its actuation axis crosses the CoM. The second attached craft shows the glitch by actuating a hinge.
In actual use, this glitch came up quite quickly after Deploy Limit was usefully added to axis groups:
The trigger for the reversal of direction is not so easy to see, however, in that natural use-case.