I had 6 transfers (call them f1-f6). I have my max connections set to 1, so only f1 was transferring, the others were waiting.

I decided I didn't want f6, so I clicked on it then clicked Stop. Instead of stopping it, f2 started transferring, so I now had 2 transfers going at once (despite a max transfers of 1). f6 still shows as waiting, and I can't remove it from the list.

In addition, when f1 finished, f2 was still transferring, but it started f3 transferring, against despite a max transfers of 1.

I then tried stopping f6 again. Now it says Disconnecting <server>, but I still can't remove it from the list, and f4 started, so I now have 3 transfers going.

It appears that whenever a transfer ends, either because it's finished or I stop a queued transfer (even if the stop doesn't work), Cyberduck just starts the next transfer. It seems it should check the max transfers before starting a transfer and not start it if max transfers would be exceeded.