That’s exactly it. I think it would be fair to classify this as a bug, unfortunately it is quite complicated and expensive to do more sophisticated C++ parsing of the string expression to figure out whether it needs a return or not. I hope one day someone better than me at parsing C++ will come up with a solution, for now we cannot but live with this limitation
I completely agree with you and @FoxWise that this behavior should at the very least be clearly documented, I opened a pull request here.
Thank you for the feedback and sorry about the problem!
Enrico