I forgot where I saw it, but amsteel loses a lot of it's strength when pinched (ie: in a knot). It's why whoopie slings are so popular: they don't have knots just buries and loop-locks. I've even been a bit leery of the figure 9's i've seen because of that fact.
No knots for amsteel.
PS: (if that's not what is going on, disregard the post. Just didn't want to leave you hanging.)
PPS: (reading back through and: the puns are unintentional.)
Knots derate any line. It doesn't derate amsteel any worse than any other line. Amsteel is not covered, so chafe can be a problem for long term usage when compared to a covered line. Chafe is also magnified by the thin diameter. Amsteel is slippery, so it does not hold knots as well as other lines. Knotting it is OK, not preferred, but OK. I don't hesitate to knot it when I need to. I will usually add a safety knot, a figure 8 or something to reduce the liklihood of failue if it were to slip if the loading is critical.