CH.LEN and Chain sequencing problem

I have pattern with different track lengths and scales, call it PTN3. I’ve set CH.LEN to 64 and M.LEN to 256. If I chain together PTN2-PTN3-PTN4, then PTN3 plays for 64 steps, as it should.

If I duplicate PTN3 in the chain, then it does not play as expected.

Chaining together PTN2-PTN3-PTN3-PTN4 causes PTN3 to play for 320 steps. I would have expected PTN3 to play for 128 steps.

I think this is related to a bug in the earlier versions of the code. I’m running v1.11d.