Kwrite is unable to open a file passed as argument, at least in my Lubuntu 16.04 box. Version of KWrite is 15.12.3. If you type in command line "kwrite file.txt", with "file.txt" existing, then it shows the name of the file in the window bar, but it does not open the file, showing a brown rectangle which reads "new file", instead. This means that if you choose a file from the explorer, right click and choose "open with...", and then kwrite, it happens the same described above. The documentation does not warn about a special way of opening files, so this must be a bug.
Exactly the same behaviour found in Kate 15.12.3.
This should be fixed in 16.08 (and master)