[2.3.0.124 C7] Odd "invalid" message in rule

In an RM 5 rule, I'm seeing an odd "invalid" message after a substituted variable name.

Inserting the same line into that rule generates the same "invalid". And, I'm seeing it on all the RM 5 rules that use a variable to set the volume. However, the rules seem to function as expected.

Creating a new rule with RM5.1.1, however, doesn't show the "invalid".

Thoughts?