You have to leave off the $ or % or # when doing an assignment for some odd reason. Probably just a parsing issue which needs fixing, so yes it is a bugette and so is this, as the compiler should really complain.
Type any
Field a$[10]
End Type
a.any = New any
a\a#[1] = 123.45
Print a\a%[1]
WaitKey()
Type any
Field a$[10]
End Type
a.any = New any
a\a#[1] = 123.45
Print a\a%[1]
WaitKey()