tldr, if you port from KApplication to QApplication, remove the %i from the Exec lines of your .desktop files.
Hey all, so I've been running plasma-next on my main development machine for a month or two now and have definitely enjoyed the speed at which improvements come. Just in time for plasma 5.1 release timezone support was added to the digital clock, so you can choose which timezones you want to see, use your mouse scrollwheel to change which one is visible, and so on. Also because our translators are awesome we got a last minute change in after the string freeze with their permission to show all the configured timezones in the clock's tooltip (similar but not identical to how it worked in kdelibs4 based plasma times). I enjoy the new Breeze theme and icons, and the alternatives system for switching between different k-menus, different task managers (I'm currently enjoying the icons only one) etc. is so handy.
In other news something that has been bothering me for a while is that okular just didn't want to get launched from any visual launcher. Clicking on a pdf in dolphin acted like it was launching, but no Okular ui would appear. Clicking view book on pdf books in Calibre would do likewise. So I spent a couple of days adding debug messages to kinit and klauncher trying to figure out what was going on. Kate launches just fine, so I tried copying the kate.desktop to okularApplication_pdf.desktop and replaced kate with okular etc. and that worked fine also.
So today I asked Albert if he had any ideas and got thinking it had to be something in the .desktop files themselves. So I uncommented another qDebug line in klauncher that said exactly what it was asking kinit to start and found it using "/usr/local/bin/okular blah.pdf --icon okular. So I tried the same from a terminal and found that okular's binary failed to launch because it doesn't understand the --icon parameter. A bit of digging found that KApplication handled that argument, while QApplication doesn't and the frameworks port of okular like a good example ported from KApplication to QApplication already.
Klauncher puts --icon blah in when you have %i in the Exec line of the .desktop file. So if you port from KApplication to QApplication, be sure to remove the %i from the .desktop files of your application also.