Anyway, the scabby workaround for me is a little script which simply kills and restarts a pair of Lexmark driver services:
$ cat ~/bin/restart-lexmark-x4550.sh
killall "3500-4500 Series Button Monitor"
open "/Library/Application Support/Lexmark/LexmarkNetworkServices.app/"
open "/Library/Application Support/Lexmark/3500-4500 Series Scanner.bundle/Contents/SharedSupport/3500-4500 Series Button Monitor.app/"
This seems to do the trick. Of course, it would be better if Lexmark would fix their drivers, but after the last phone calls I had with their tech support I don't think this is a big priority for them (it was an outsourced-to-India tech support line, where the guy did almost everything he could to pronounce that it was a problem with my router or my computer or something, rather than actually passing on information about a probable bug to the dev team... although he did seem to have a decent technical grasp of the troubleshooting steps he performed which makes him infinitely better than the Acer helpline which appears to go to a call centre in Scotland with lots of ignorant people in it. Whoops, my comment in parentheses is longer than the preceding paragraph, boo!).