is this once the bike has warmed up or just after start-up (and for about 10 mins)?
If it's on start-up, most 748-996 do this. Something to do with the oil taking longer to get to the rear cylinder. Hence all the advice to warm-up before moving off.
If all the time then could be something else. Mine does this on start-up but both pipes run clean after 10 mins or so.