When I click on a link to a pdf document I'm given a "Save As" dialog box. On previous versions of K-Meleon the document would open in the browser window using acrobat reader. However, if I go to "about:plugins", then go back and try to open the pdf it works fine. I'm assuming that KM's not properly loading the plugin until it does some kind of plugin scan for about:plugins. I've been able to duplicate this bug with both Acrobat Reader 5.1 and 6, on Windows 98SE, 2000, and XP, with a fresh install of the OS, KM, and plugin in the case of XP. I've also tried installing KM then the plugin, and vice versa, with no difference.
I don't know when this bug materialized, but it was some time into the beta 0.8 process.