The attached script propagates 3 spacecraft. All three start from the same initial state. All three propagate correctly for the first 0.1 days. All three turn on a thruster at that point. The thrusters have different thrust magnitudes, but all point in the velocity direction. At that point, the spacecraft display as no longer coplanar, even though they are physically coplanar.
Note that when the bad plotting occurs, the center of the bad trajectories is not the center of the Earth.
The script propagates to an RMAG value, and turns off the thruster when that value is reached. As can be seen by running the script, the final spacecraft orbits are again coplanar when all is said and done. But there is something wonky in the middle part of the propagation taht makes GMAT present invalid data.
A screen snap is also attached. I see this behavior on Linux and Windows. Have not checked Mac.