Evaluation of optional composed rule elements not working correctly

The evaluation of optional composed rule elements is not working correctly. Example:

Input:
some data : 20,20
some more data : 20
and again : 20,20

Rule:
ANY+? NUM (COMMA NUM)?;

This rule is not matching on the second line. The evaluation of the composed rule elements terminates too early since no comma was found. However, the complete expression should be optional.