It may be a bug, although I don't expect it is. If you have multiple operating points, it is very hard to guarantee which you will get - the slightest little thing can cause it to roll down either side of the mountain into the two valleys (to use an analogy).
Restart does start the op point from scratch, but it is using the matrix built from the previous run, and so the ordering within the matrix can affect the solution. Rebuilding the matrix usually then forces the sim to start from scratch.
That said, if you are doing a dc sweep vs a parametric sweep of dcOp (I can't see the previous posts in the threads as I'm travelling), that could explain it. The restart won't cause it to reset within a DC sweep (I think - it's primarily for how it handles a dc sweep within a parametric analysis or sweep analysis, rather than between the points in the sweep) and rebuilding the matrix won't help.
I don't think there's an easy solution other than the one you've done.