If I remove the Text to Speech Device when editing a RM 5.1 rule, the volume for that previous device still appears to display.
It looks like the volume setting doesn't get removed when you deselect the Text to Speech Device. This might be more cosmetic more than anything but figured I would post it since I just found this issue.
Here's how it looks after I edited it:
If I select the Text to Speech Device again, I can see the previous setting of 60 displaying:
Here's the display after saving the changes even after I save the rule and go back in:
The solution I found is enabling the Text to Speech device and just delete out the volume.