During a build, we're seeing this in the console output, but it doesn't appear to impact the actual execution. We get what we wanted:

Build step 'Conditional steps (multiple)' changed build result to SUCCESS
Regular expression run condition: Expression=[*.Windows.*true], Label=[Windows,Linuxfalse]
Exception caught evaluating condition: [java.util.regex.PatternSyntaxException: Dangling meta character '*' near index 0
*.Windows.*true
^], action = [Don't run]

We get this consistently. We have a checkbox to run tests when it is checked. We only see the above when it is not checked.