Does Sync Symbols just not work at all with classic tweens? Does it do anything at all?

The title says it all. 

I could swear that, once upon a time, Sync Symbols worked as I would expect - keeping symbols in sync -  but now it doesn't seem to do anything at all.

Example -

1. I make a graphic symbol which is a gear, rotating clockwise. 
2. I place the symbol on the timeline.
3. I make a keyframe at frame 50.
4. I make a 2nd keyframe at frame 70. 
5. I create a Classic Tween between frames 50 and 70.
6. I check "sync symbols" in the Tweening properties.
7. At frame 70 I re-size, or move the symbol.
8. Placing the cursor between the two keyframes, I hit F5 a few times, lengthening the tween.
9. The symbol now "jumps" at the end of the tween. It is no longer in sync.

This is exactly what happens if I leave Sync symbols unchecked. Either way, the symbol falls out of sync.

If I do the same thing using Create Motion Tween, the symbols stay in sync whether I check Sync Symbols in Tweening properties or not.

Have I just forgotten how this is supposed to work?  I'm attaching an example file.