Params are passed by reference. The elements of @_ are aliased to the arguments passed.

>perl -le"sub f { $_[0]=456; } $x=123; f($x); print $x;"
456
[download]

>perl -le"sub f { $_[0]=3; } $#a=2; f($#a); print $#a;"
3
[download]

it seems that those in the know are trying to fix it appropriately (or have already done so).

I wrote a fix. It was reviewed by Rafael who fixed a big in it and committed it.