document delivery issue

Hi ?
I have a requirement, there are two IS nodes (not cluster, not share um client prefix) connect to one UM and the IS have the same packages, I want to publish one document and need only one trigger process the doc. So I use the pub.publish:deliver flow service and the destId is set to IS default client. Actually, one trigger is process the document, but in the UM enterprise manager, I find the document is in the queue of another trigger.
I’m confused that I just send the document to one IS, why the other IS have receive the document.

UM version is 9.12