AEC learning behaviour

Hello,
We've integrated the speex echo canceller into PulseAudio, and coupled
with the AGC/denoiser, it works reasonably well and has been a breeze to
plug in, so thank you!

One thing we're seeing, though, is that the canceller seems to take some
time (a few seconds) to "learn", so initially the echo is clearly
audible and it slowly fades out. This sometimes occurs in the middle of
a call as well (the echo becomes loud again and fades away in a few
seconds).

With the echo suppressor enabled, the learning time seems to drop, but
the final echo remains higher than without suppression, and is still
sufficiently audible to be annoying.

Is this known behaviour? Any clues w.r.t. what might be going wrong?

Cheers,
Arun