I seem to recall having a couple of times where an * isdupe invocation was required.
This morning I called dupe on a video, and instead of waiting for someone else, siftbot wrote:

This video has been declared a duplicate by the original submitter; transferring votes to the original video and killing this dupe - dupeof declared by demon_ix.

This video has been nominated as a duplicate of this video by demon_ix. If this nomination is seconded with *isdupe, the video will be killed and its votes transferred to the original.

Note - I wasn't the original submitter of the video.
After that, the video was duped, and didn't wait for an isdupe invocation.

Is it broken, or am I missing something?