The ui slider node has a checkbox labelled 'If message arrives on input, set slider to new payload value`. However, for me, the slider position on the display seems to always be updated by a message, but the select box actually controls whether a message is sent or not. So it performs like the Pass Through checkbox on the Switch. I believe the behaviour is correct but does not seem to match the words in the config dialog.
In addition, in the help text, it says
"Note: An input msg to the slider node will not change the status information displayed unless the slider node output is connected to another node."
That does not seem to be correct, whether it is connected to another node does not seem to affect the status display.
I am running node-red 1.2.2 and dashboard 2.23.4 with Waterfox browser.