I recently started noticing the problem on two months old GS 150. I have the service manual for this thing so I looked up in its troubleshooting list. Things ranging from missing valve adjustment to dirty air filter to carburettor blockage to plug clearance to CDI, were listed in problems with idle speed and stalling causes.
None of these looked like probable sources to me, specially the air filter and plug, both of which were perfectly cleaned in last tuning including the valve adjustment.
So I started experimenting with the choke. Like @fanno__ I was having this problem for first 4-5 kilometres. But after giving it a choke of 3-10 seconds on first cold start of the day (I mostly go to work in noon), there's no missing whatsoever for rest of the day!
May be things have started to change as winter is approaching or may be it is because of the thick Liquy Moly oil that I am using. Whatever the fact, I do push this thing to the limits on highways