I am on Kubuntu 15.04 with Plasma 5.3. I am really sorry, I am not sure what I installed, however, there are some inconsistencies in my application right-click and file open menu styles. For instance, system settings does not use the file open dialog the rest of my applications use, and the menu style in Gwenview is different than in Okular. I realize how vague this is, since I am not sure what I installed, but any idea on what I can do to have applications all use the same style would me much appreciated. Here is a screenshot of the file+open menu in okular vs system settings.

http://imgur.com/lxddaMO

Well, that wasn't so hard to figure out. My apologies. The problem was that I installed appmenu-qt and appmenu-qt5. It seems that installing them messes up the theme in some apps. After removing them things are back to normal.