[quinta@ebf.cz]

One more discovery:

When guide reference type="cover" points to html which is not first file of reading order (you can see order of files in file list of editor, or in spine section of opf), "Go to" menu item is created "as expected" (on the top of list, and with name as defined in title).
Of course cover page shoud be first file of reading order... So this just indicate that the menu creating process is influented by something else then the guide item type itself.