X3: How to change bar time sig without having clips change their musical position?

Use case: I have an existing project with a section mostly in in 7/8, with some 4/4 bars for variety.

After some rehearsals, I realize that for the solo to work, I need one of the 7/8 bars to be in 4/4  time (bar 24).
If I just change that one bar to 4/4, all the subsequent clips change their musical position:

Notice the clips in bar 25, 26, 27, etc are now all offset. Clearly not what I want. (I used the Click Track to make it very obvious that this is undesirable.)
 
OK. I don't know why that should happpen - the clips all use the default timebase of "Musical"; they are not locked to "absolute" time...
 
OK, so let's UNDO that, and try locking the clips first:

Still doesn't work.
 
Now, I don't think the clips should need to be locked at all, but even if they do, the help file seems to indicate that the clips should not be changing their M:B:T position if they've been locked and the timebase is "Musical":

If the clip is set to the Musical time base, the clip’s M:B:T position stays constant, and its Absolute position shifts. If the clip is set to the Absolute time base, its Absolute position does not move, but its M:B:T position shifts.

So - what's the deal?

• Do you think this is a bug?
• What is the recommended way of dealing with this situation?

 
I'm using Sonar X3 Producer.