Wierd sorting bug?

[Franz Huber]

my MySQL Server (version: 5.0.51a-3ubuntu5.8) I have the following InnoDB table:

http://pastebin.com/8zXh43Zg

The following query produces wrong (wrongly sorted results):

SELECT id,kontostand FROM `kontostaende` WHERE konto = '1' ORDER BY id DESC LIMIT 5

It will show rows sorted ascending by id from id=1 to id=7.

If I change the query by doing any of the folloginw changes:
- "LIMIT 5" -> "LIMIT 6"
- remove "WHERE konto = '1'"
- remove column "kontostand"

the result will be rows sorted descending starting from "id=8".

What is wrong here?