When overloading binary operators e.g. '+', perl calls the overloading sub/method with 3 arguments - the 2 operator arguments (as objects) and a flag indicating whether perl has swapped the 2 arguments before calling the sub/method (see overload - as you probably already have :-). Therefore, your use of rmvObjRef() is incorrect in this context.

Consider:

use NumObject;

my ($a, $b) = (NumObject->new(), NumObject->new());

my $c = $a + $b;
my $d = $a->addObjects($b);
my $e = NumObject::addObjects($a, $b);
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In the above, the assignments to $c, $d & $e result in slightly different invocations of addObjects(), but will all have the same post-run value - assuming the call to rmvObjRef() is removed/commented out.