I've noticed this because a plugin I developed for Atto, needs to get the Atto textareas content. For that, I do the following:
which works for almost all the cases, except for those HTML elements that have non-valid characters in their id attribute. And the quiz activity is one of those.
When trying to grade a quiz answer, I noticed that the "Comment" textarea have id values similar to this:
Being the colon a non-valid HTML attribute character. And, the Y.one returns a null object.
I've opened a ticket in the tracker also: YUI creates non-valid characters for HTML attributes in quiz activities.
I don't know if there is any good reason for this, but any Atto plugin trying to get the textarea by the that one, will result in misbehaviour. In the plugin I mention, for example, the form is never submitted.
For the moment, I will make the plugin check every textarea of the page finding illegal characters, not to add it to the toolbar if exists any, but I guess that this is something to fix in the core.