Sliders and incoming messages

I have a set of sliders that control some servos remotely. The servo values all get bundled into one http request, so I have a node that hangs onto the state.

I'm seeing strange behavior - sending a message with any topic to the input of the slider causes the slider's value to update, and the dashboard UI to update. BUT, the slider doesn't send the message on unless the topic of the message matches the topic of the slider (when the pass thru message check is checked).

This seems inconsistent to me. Shouldn't it either demand a topic match or pass on the message whatever the topic?