Ah, it's not a bug, it's because the command is being parsed twice after it's generated: First by MS-DOS and then by Opus.
Try using two " instead of "' and '". If that doesn't work try using three, and so on. MS-DOS does strange things to quotes sometimes but it usually starts to work if you add enough of them (but not too many 
). Usually you only need two.
Something like this should work, although I haven't tried it:
@nofilenamequoting
dopusrt /cmd CreateFolder NAME=""{destpath}{file$|noext}""
The doptest tool by Tanis is good here for checking the command that you're generating after it's been processed by MS-DOS.