You are right.
This is an error message, probably by your question validation.
I can only reproduce your screenshot by
- setting "Hide tip to "OFF"
- entering a question validation like "count(self)>0"
- entering a validation tip like "Please select one answer"
If you set "Hide tip" to "ON" and setting the question "mandatory" you get
But in this case you do not need your question validation, because you have to select at least one answer (mandatory).
You did not say, what exactly you want to achieve.
At least one answer? This you get by setting "mandatory"
Exactly ONE answer? This you get by setting "Max. answers" to "1" and hiding the tip.
You see you only get the error message.
If I misunderstood your problem, please explain.
Joffm