This is normal. With two batteries in series the voltage is always over the LED Vf and it’s easier for the driver to maintain max output.
The M22 is compatible with 2xRCR(18350). You can use them without concerns.
Congrats to your choice. M22 is a very good flashlight. 8)
The only problem I had(two times) with it is loose retaining ring(on the tail cap).Check it often.