There are words that are considered to be wrong by Flyspell that are instead considered correct by Ispell. I thought that Flyspell was merely an async version of Ispell, I must be wrong...
To add to the confusion, there cases in which
ispell-buffer finds nothing, but
ispell-word instead considers some words in the buffer to be wrong, coherently to what Flyspell has to say.
Here's an example:
$ echo http://example.com >/tmp/test
$ emacs -Q /tmp/test
M-x flyspell-buffer. The word
http is now marked as wrong, in fact,
ispell-word shows the usual interactive menu. Yet,
M-x ispell-buffer completes without finding any wrong words.
Can you help me understanding what's going on here?