[Elecraft] KPA1500 reduces power as it gets warmer?

[David F. Reed]

I note my KPA1500 drops power at its temperature rises...

Using FT8, so a relatively high duty cycle.

Say I start at a heat sink temperature of 27 C, and 1,000 watts out; by 
the time the temperature is at 65 C, the power has dropped to 893 watts out.

I have a couple of questions about this (not a complaint by the way):

 1. Does anyone else experience this?
 2. Is it normal?

-- 
Thanks & 73 de Dave, W5SV