[Elecraft] KPA-1500: Strange Symptoms on FT8

[Pete Smith N4ZR]

I've been operating 160M FT8 recently, and am noticing some odd symptoms 
from my amp that seem only to occur in FT8 mode.  Even running only 
about 1170 watts into a good dummy load, with the KPA-1500's ATU 
bypassed and a displayed SWR of 1.0:1 during transmit, as soon as the 
transmission ends both the display on the amp and the KPA-1500 utility 
show SWRs ON RECEIVE  of  1.6-1.9:1.

I just tested on 80 meters, and am seeing the same anomaly on FT8. This 
does not happen on CW.

The question is, where is this spurious reading coming from, and should 
I be concerned?

73, Pete N4ZR