I think that might be "Once Upon a Time".  I think that I read that they are compatible now.

Besides, don't tell my engine about that.  It didn't get the memo.

Don't believe all the crap some self proclamed specialist is telling. If You go to any store You will find "synthetic blend" oil. This should be enough.
If You want a better example, just mix in a clear cup the 2 kinds of questionable oil and if they don't separate, You should be OK.
I have been told the same things about mixing different vicosity oils, and about mixing oils from different manufacturers.
Don't forget that even in the "regular" oils, You have synthetic additives.
If You do some research, You will find, that there are only 3 real synthetic polyalphaolefin oils / Mobil 1, Amsoil, and one other, that I keep forgetting/, and Red line is esther based synthetic oil. The rest of the oils are in reality very highly refined petroleum based oils. I know it doesn't sound right, but whoever doesn't believe, let him do some research.
The thing is - WHY would You put the inferior regular oil if the prices are so close and if the bike takes only 2 Qts of oil?

georgekathe wrote on 12/31/69 at 16:00:02:
I have noticed this very thing. I just put synthetic fluid in my vl 800 it takes 3 and a half quarts, and when i start it up it really sounds like the valves are ready to come out. now suzuki doesn't recomend  synthetic but rather just 10    40 or 15   50    with the jso or whaterver the japaneese thing is or a another high grade oil. i just think all that valve noise can't be good for the bike.

I've known a couple of HD guys who really wanted to go synthetic and when they put it into their bikes, they leaked like seives.  Both of these guys used Royal Purple.  One of them is now using a synthetic blend and he says his bike doesn't leak any worse than with dino juice.  The other huy just went back to Rotella.  I've never tried Royal Purple.  I've only used Mobil1 V-Twin 20W-50 and Maxum4 Extra 15W-50 and have had no problems on my 98 LS650.

In the for what it's worth dept.: my experience has been that engines that leak a little will leak more with synthetic. I have used synthetic in my bikes for years and never had one leak yet.  I have no fear of mixing modern engine oil and do so all the time.  There are a lot of engine oil myths out there, that's for sure!

Yes indeed, lots of myths and urban legends out there about oils.  In the real old days air-cooled racing engines would use castor bean oil that IS incompatible with petroleum (mineral based) oil.  These days common synthetics like Mobil 1 (PAO or poly alpha olefin base) or Motul (polyester base) are fully compatible with oil refined from crude oil petroleum base stock.