Where does mapping come from on Windows?

While looking into a different issue, I found that my Windows gvim has a mapping defined for pasting with <S-Insert>, but not my Solaris gvim.

I did ":verbose map <S-Insert>" and got:

v <S-Insert> "-d"*P
n <S-Insert> "*P

To my surprise, there is NO "Last set from..." message telling me where the mapping is defined. So...where IS it defined? When this happens for an option setting, it means Vim set it that way by default or I typed it manually. What does that mean for a mapping? And where is this mapping actually defined? And why only on Windows?

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