This could be normal. The behaviour of the XT600's oil system is governed by some wizardry.
1-In short, what happens at cold start is that the oil is pumped by one of the oil pumps into the engine from the oil tank. for some reason unknown (yet) to me it takes a while before the other oil pump starts pumping it back into the oil tank. Consequently, the oil level in the sump rises and might lead to the phenomenon you describe. Although I think it is pretty extreme what you have here.
2-What also could happen is that the primary oil pump (the one first referenced to in this text) is worn in combination with a leaking check valve at primary pump outlet. At standstill, and higher ambient temperatures, the oil seeps slowly from oil tank to sump.
3-Far to much oil in the oil system.
To check 1 and 3: Drive the bike around for about 30 minutes, normal start-stop etc. Check oil level after 10 seconds of idling, then stop. Level in oil tank should be OK, level in sump should at least be below the stop. If level in tank is OK and level in sump is OK, no worries. If level in tank is OK and level in sump above stop, see case 3: drain oil.
Check 2: Check oil level as described in check 1 and 3. Let bike stand for extended period. If level in tank has fallen significantly and level in sump has risen, it's case 3. Replacement of check valve and / or oil pump through removal of r/h cover and clutch (pump only).