A question regarding Smart Bone Actions and control bones

[minigendo]

Greetings,

My apologies if this is has been asked recently, but I did some searching and didn't turn up anything. It's possible that I just missed it though, or that this is common knowledge.

I'm a hobbyist and have been building a facial rig. Currently I'm using the last release of 12 (I own a copy of 13 but haven't installed it yet).

While I was building my rig, I came across a weird issue that looks like it might be a bug, and I wanted to inquire if the issue is known / was fixed / had any workarounds, etc.

Rather than try to describe the rig I built and what caused the issues, I'll describe a simple file I created to replicate the issue.

I have a file that contains:

Bone layer a. (smart bone with smart action)
Vector Layer 1 (shape)
Bone Layer b (control bone , smart bone with smart action)
Vector Layer 2 (shape, bound to control bone)

Bone Layer b contains a control bone (please excuse me if I'm misusing the terminology) bound to points in vector layer 2. It also contains a smartbone with accompanying smart action. The smart action moves (translates) the control bone between two point (moving the shape that's bound to it).
Bone Layer a contains a smart bone with accompanying smart action. The smart action manipulates some points in vector layer 1 and manipulates the smart bone in bone layer b. On frame 0, this works exactly as expected. Manipulating the bone on bone layer a causes the shape on vector layer 2 to move.

On frames 1 - whatever, this doesn't work. Moving the smart bone on bone layer a will move points on vector layer 1 and cause the smart bone on smart layer b to move. However, the control bone does not move (or at least the shape it's bound to doesn't).
Moving the smart bone on bone layer b independently (not through bone layer a's smart bone) will work as expected.

If I alter the setup such that Bone Layer B's smart action doesn't manipulate the control bone, but instead moves Vector layer 2's points directly, it works without a problem.

I think I can work around the issue in a couple of ways, but it's not intuitive to me why this doesn't work. Can anyone offer any suggestions?

My thanks for your time and apologies for the trouble.