That's weird. By "method variable names" I mean local variables, i.e. those declared inside a method.
I'm not getting the same results as you with a little sample program I wrote - see: https://gist.github.com/JosephRedfern/662131ceb2119abf3e83. Field names and method names are preserved (which make sense), but local variable names are lost (which also makes sense to me!)
Are you sure that your example code doesn't include debug information?