Target wiki for the copy document action is always current wiki id instead of the id of available wikis.

When in virtual mode, if you try to copy a document, the 'target wiki' select field will have N options (N=number of wikis in your farm + 1 which is the main wiki) but all options have as value the current wiki identifier.

This makes it impossible (using only the UI) to copy a document from one wiki to another.