In my experience both vi and vim yank (change/delete) into the "default" buffer every time a yank (change/delete) occurs - even if the yank is performed with a named buffer.   So if I use "ayy to yank a line into the 'a' buffer, I can "put" that buffer back using either "aP or just P, the latter using the default buffer.  Right now the default buffer only seems to hold the items explicitly put there and that is not the same as either vi or vim.  Is there a way to change this through the configuration settings?