sprintf and pack can trigger the 0+ overload

Now that you mention it, I do recall experiencing that overloading with sprintf(), but I failed to recognize it for what it was.
"How the hell does that work ?", I thought ... and then quickly replied "Gee, that's handy !" ... whereupon that particular conversation with myself was abruptly ended.
For anyone seeking an example:

C:\>perl -MMath::GMP -le "printf '%x', Math::GMP->new(10);"
a

C:\>perl -MMath::GMP -le "print unpack 'H*', pack 'I>', Math::GMP->new
+(254);"
000000fe
[download]

Cheers,
Rob