Bone with TrackTo constraint isn't rotating properly in poses on 1st frame [video included] See video example here: Watch Video on YouTube

My problem is that, in pose mode, when I'm in the Action Editor, the initial pose of the bone (that controls the lower cylinder of the excavator/construction vehicle) is off. It's not what the keyframe has it set as. Attempting to rotate the bone or move forward in the timeline, however, puts the bone back to its proper rotation. It's only when switching between Actions that this off-rotation issue appears. The problem is the issue is continuing into Unity, the game development program, and messing up the animations. My expected behavior of the bone is that it wouldn't glitch on the 1st frame of the Action when I switch between actions.

Here is a screenshot of the TrackTo constraint I have on this bone, targeting an object above it near the upper-cylinder:



Here's what the bone &amp; cylinder should look like from starting frame:


Here's what it actually looks like when I switch between Actions (this glitch also carries into Unity):


Does anyone know how I can fix this problem? Any help would be greatly appreciated. Thank you!
Thanks to comments in the original post, I was able to find the problem and create a fix.

THE PROBLEM: 
In this case, the bone with the TrackTo constraint was targeting a mesh object (a cylinder) which was a child of the armature, creating a circular dependency and producing the error I was experiencing.

THE FIX: 
Positioned in the same place as the cylinder that was being targeted is another bone controlling the upper part of the excavator mechanism. I changed the target of the TrackTo constraint to that bone above it, thus eliminating the circular dependency. Now, even from frame one, the rotation of the bone with the TrackTo constraint is right where it is supposed to be.

Thanks again to everyone for their help!