When targeting a vessel that is landed and querying various Target data in a custom window, MechJeb will throw getObtAtUT result is NaN! constantly, severely slowing down the game until the custom window making the query is closed.

The good news is that the windows are successfully shutting down when closed!

Target data used in the custom window were:
*Time to Closest Approach
*Distance at Closest Approach
*Relative Velocity at Closest Approach
*Relative Velocity
*Distance
*Relative Inclination

Active Vessel was on an escape trajectory around the mun. Target vessel was landed on the mun, but too far away to be loaded in memory.