Maneuver node changes during maneuver

[UH60guy]

I'm getting this with and without using MechJeb. MechJeb and Alarm Clock are my only mods. 

I plan a maneuver with advanced planetary transfer, and the node shows up as usual. Plot looks good and leads to an intercept.

Whether I have MechJeb do the "execute maneuver node" or I do it myself with just SAS heading hold, I get about three quarters through my burn when several things happen instantly and simultaneously. First, the targeted planet is un-targeted. Next, the maneuver node pops instantly to a new heading several degrees away. Third, the delta V required jumps up to a few thousand m/s to some seemingly random number (maybe the original dV?). Obviously if SAS-follow-node or MechJeb is on, I'm thrown way off course as they follow the new node to nowhere fast. If I free hand it and just hold the original heading, I have to guess my way to engine cutoff, as I'm now no longer pointing towards a node and my dV countdown is inaccurate.

This only happens during interplanetary transfers- in system works fine. It happens on every ship, not just one in particular.

Any ideas why a new maneuver node is created mid maneuver? If needed I can upload a video- it's a large file and I'd rather see if this description suffices first.

Thanks!

Edited April 15, 2017 by UH60guy