Using 1.12 master from May 2014.
I have had a situation where syncing from left to right yielded the correct phase adjustment, whereas syncing from right to left produced a minor phase offset.
I could do that reproducibly, i.e. when I pressed the left sync button the two tracks were synced perfectly, but when I then pressed the right sync button, the two tracks were *slightly* phase-shifted. When I then pressed the left sync button again, they were perfectly aligned again, and so on... back and forth.
I have had this before but did not investigate properly. This time, I tried to reproduce it with the same two tracks over and over again, and could reproduce. However, after Mixxx restart *I could not reproduce using the same two tracks*. Looks like some of my actions in the course of a Mixxx session brought Mixxx into this "malicious" state. I have no idea what that could have been unfortunately.
This asymmetry contradicts my understanding of how the underlying implementation should work -- in my naive view, this operation should be entirely symmetric, i.e. we have two markers and phase adjustment should align them. The difference between left -> right and right -> left should only be which of both tracks makes the "jump", but the alignment should eventually be marker-on-marker in both cases, right?
Some might ask: if left->right works, but right->left does not, why don't you just use left->right? When we have a silenced track and one that is currently playing on master, then obviously, we do not want the master one to make the jump, so the sync direction is predefined.
The music I was doing this with is electronic music, about 120 bpm. The beatgrid was set perfectly.
Are you using master sync? Is quantize on? What about keylock?