When using the ‘bk’ roll controls on feet, a leg_3jnt will flip unexpectedly upon switching FK/IK
Here I have rotated the ‘bk1_ctl’ on the foot
This is the result after switching to FK, the leg orientation is completely off
This is using the standard leg_3jnt_01 and foot_bk_01 components, but the same happens with the Epic versions as well. The foot component is set to ‘leg_3jnt_01’ on Connector
Does that use the spring IK solver? If so, you can find some relevant topics from the past by searching “leg flip” or “spring flip”:
http://forum.mgear-framework.com/search?q=spring%20flip
There are workarounds, or sometimes you can get lucky if you tweak the guide placement just-so.
I searched around didn’t see this exact issue. The other topic about 3jnt leg flipping seemed to be about rotation issues on the mid joints. This specifically is really about the foot. It’s the roll controls on the foot component that cause the 3jnt leg to flip
This is seen on the base quadruped guide included with mgear, as well. Rolling the “footFront_L0_bk0_ctl” then switching to IK results in a broken leg/foot
You didn’t answer the question. 
Whatever or wherever the manipulation is, I still suspect it’s the spring chain solver doing the actual flipping.
Sorry, this happens on both IK Spring and Rotation Plane solver, if that’s what you mean in the component setting
Perfect thanks! Helps to narrow down the bug.