I don't know the specific details of your engine but it is normal for the designer to incorporate traps so that on initial start up there is enough oil to lubricate, in your case, the valve stems. It can take up to 30 seconds for the oil to circulate throughout the engine and the cam box is last to get it. It is quite possible that the seals are slightly worn and on initial start up a small amount of oil has got past the seal lip and it is that that gets burnt. If the amount that the engine burns is acceptable to you, say a pint in 1000 miles, then I would leave well alone.
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