question about Concorde in fast mode

[aaronz28]

i have been enjoying my new Komet LTD (Concorde) which has Mullards and Bugleboy 12ax7s in it.

in the gradual mode, it is killer, but when i switch to fast, i notice some sort of odd bloom or sag.. its really tough to describe... but you can literally feel the notes expand about 1/2 second after you thwack the notes.

generally people describe Bloom as a good thing... but this sounds unnatural to me.. any ideas what it might be?

the amp sounds just killer so i don't think anyhting is wrong with it, i've just never heard this sort of thing... i'm gonna try to get a video done of it where you can actually hear it happen.

anyone else have this experience? its almost like after you hit a note or chord, the bottom end fills in... almost to the point of being muddy.