Apache logging 404's for keep-alive requests

[ABerglund]

Running 0.4.2-stable with default skin. Seeing many (several hundred daily) 404's logged in Apache. Entries are always the same:

Code Select Expand

xxx.xxx.xxx.xxx - - [14/Feb/2011:07:33:10 -0800] "GET /webmail/?_task=mail&_remote=1&_action=keep-alive&_t=1297697589810&_=1297697589810&_unlock=0 HTTP/1.1" 404 15
This is not consistent - often the same entry is logged successful, i.e. 200. Any ideas?