Download and open doesn't always work

[Technical Support]

Clicking on a link that downloads a file brings up a save/open dialog. Clicking Save works fine. Clicking Open sometimes fails. For instance, when clicking "View my bill" on the Puget Sound Energy (http://pse.com) website (after logging in to an account). The reason it fails appears to be that the file downloaded is named "latest". It is a pdf file without an extension. Once it is downloaded, it opens as expected. It just doesn't open directly by clicking "Open" in the save/open dialog.

The problem appears to be that files without an extension don't open directly though the dialog lists it as an option. Once they download, the system associates them correctly.

Midori 0.5.11 ((null)) Midori
GTK+ 2.24.28 (2.24.28) Glib 2.45.6 (2.46.2)
WebKitGTK+ 2.4.9 (2.4.10) libSoup 2.50.0
cairo 1.14.2 (1.14.2) libnotify No
gcr 3.16.0 granite No
Platform X11; Linux x86_64