The variable 'yychar' is not handled by the methods 'yypushStream' and 'yypopStream'. The appropriate code is missing in the file 'skeleton.nested'.
The method 'yypushStream' should save the variable 'yychar' too in the class 'ZzFlexStreamInfo' and then reset it to zero.
The method 'yypopStream' should restore the variable 'yychar' too from the class 'ZzFlexStreamInfo'.
The class 'ZzFlexStreamInfo' should have the member 'yychar' too and save the respective parameter in it's constructor.
The variable 'yychar' should be handled like 'yyline' and 'yycolumn' in the methods and the class.
The appended file contains my proposal to fix the error.