Ah the death stem.
Yes they failed, I don't know if there was any warning, but there
were enough cases for it to be a well known fact that certain AVA stems
failed. Below is a picture from Sheldon's site, note that the stem is hollow and
is through the entire extension, enought bouncing, jostling and stress and it's
going to tear/fail.

if you're going to take your ava stemmed bike out for gentle riding probably
won't matter, but if you are going to hammer, climb etc. I'd change it for something
a bit less prone to failure.
but what do I know, I rode a viscount with death fork for 4 or 5 years.

marty