lucy24 - 6:35 am on Mar 10, 2013 (gmt 0)
Mystifying, to be sure. Let's have the real names. If necessary, misspell something. But first test the misspelling and make sure it behaves the same as the correct spelling :) If it doesn't, you are that much closer to your explanation.*
#1 name of page that redirects to directory (You did say redirect, right, not silent rewrite?)
#2 name of directory
#3 name of some other random pages in same directory that behave as intended
Did you get any information from Live Headers? Save the result to a text file so you can spread it out and read at your leisure.
* Earlier today I spent several hours trying to figure out why the latest piwik didn't work. The problem turned out to be a line of seemingly unrelated code ... which, if absent, would have prevented the earlier versions from working. (And in fact did prevent them from working in several directories. All this time I thought I just hadn't got around to installing the tracker.) I do not pretend to understand this. But Live Headers definitely got a workout.