I can't speak for your 450, but my FTdx-3000 does this when activating the tuner's 'tune' function, and sending a 100w carrier in CW mode:
Power output has a fast spike to the 10w level, then bobbles about the 2-3 watt level whilst tuning.
Note that there is a menu setting called 'EXT AMP TUNING PWR', which is menu item # 178 in my rig, and I have it set to 10w. My choices being 10, 20, 50 and 100w.
Chuck, N8NK