The expression parser is not working correctly on a worksheet formatted to use R1C1-style references.

For example, try entering the expression '=CONVERT(1,"m","m")' -- you get told this is an invalid expression.  This happens whether you use the expression entry widget, or if you build that expression using the formula guru.

The problem is in the parser; the first token generated in yyparse() is a RANGEREF, when it should be a STRING.  This is happening when r1c1_rangeref_parse() is called -- as 'C' is a valid cell reference in R1C1 style (the entire column of the current cell) it is interpreting it as such, so the RANGEREF token gets generated.

For a fix I guess that r1c1_rangeref_parse() needs to check the following character after the cell reference to see if it is legal (one of [-+*/(),=<>\0] plus maybe a few others).  Or maybe something else; I'm really not sure what would be the right way to do this.