This bug is already in KTorrent for so long.

How to reproduce:
* Have two torrents of size 6GB or more each.
* Load the first one through the web interface and wait
* Load the second one through the web interface
* The load of the second one is very long and KTorrent crashes right at the beginning of the creation of the file(s) of the second torrent.

Edit: This is especially true if you exit the browser after loading the second torrent (without waiting for KTorrent's response to complete).

I will see if I can reproduce it.

Note: I have ext3 as my file system.
I hope that info can come in handy.