I am not able to reply to some comments on Rietveld. When I tried to reply to
the comments by loewis at http://bugs.python.org/review/6715/diff/3335/10393, I
get an error saying "Error: AssertionError; please report!". This takes the form
of red text replacing the comment I was replying to, and appears after I enter
my reply and hit "Save".

This does not happen if I first try to enter a reply to one of the previous
batch of comments (by amaury.forgeotdarc) first, discard it, and then reply to
one of loewis's comments.

This may be related to issue 402 - I am still not able to sign in to Rietveld
without temporarily changing my username.