There's nothing special about those functions. The magic is Perl acting as if UNIVERSAL was in @ISA when doing a method call. Apparently, can doesn't. Bug!

>perl -wle "{ package UNIVERSAL; sub test { '!' } } print I->can('test
+')?1:0;"
0

>perl -wle "{ package UNIVERSAL; sub test { '!' } } print I->test;"
!
[download]

that neither the argument nor the return value of can matters in that snippet.