Overloaded operator handlers sometimes receive operands in reversed order, but Perl will notify the handler when it does so by setting the swapped argument to true.
Three arguments are passed to all subroutines specified in the use overload directive (with one exception - see nomethod). [...] The third argument is set to TRUE if (and only if) the two operands have been swapped. Perl may do this to ensure that the first argument ($self ) is an object implementing the overloaded operation, in line with general object calling conventions. [...]
You probably disregarded that argument?