If you look in your events.log you will be able to see what commands the UI sends to your openHAB Item.
We’d expect UP and DOWN of course.
There is no guarantee that any particular device supports all the possible commands, it’s up to the binding to translate openHAB standardized commands into something the device can handle.
This looks relevant -
You can probably workaround this issue using a Switch sitemap widget with mappings=[ ] to create “Up” and “Down” buttons that actually send numeric position commands 0 and 100. Or perhaps 99, read that thread.