In dolphin, if you use right click -> create new -> text file, you get a text file and are allowed to give it a name.  However, for many extensions this creates automatically appends .desktop to the end of the file instead of using the extension you specified.

Steps to reproduce:

1. Open dolphin
2. Right-click on a blank space
3. Select "create new"
4. Select "text file" (or any other normal file, folders don't have this bug)
5. Create a file test._, where ._ is an extension.

Expected results:

An empty text file with the file name and extension you specified is created.

Actual results:

Here are the results for specific examples.  The filename I gave is first, the filename that is actually created is second:
test.manifest
test.vtt --> test.vtt.desktop
test.ics --> test.ics.desktop
test.css --> test.css.desktop
test.cssl --> test.cssl.desktop
test.csv --> test.csv.desktop
test.htm --> test.htm.desktop
test.html --> test.html.desktop
test.a --> test.a.desktop
test.c --> test.c.desktop
test.cc --> test.cc.desktop
test.cpp --> test.cpp.desktop
test.gv --> test.gv.desktop
test.m --> test.m.desktop

This bug appears to be triggered mostly when the extension is of a text file mimetype known to KDE, except for those of the "text/plain" mimetype, as well as some (but not all) other mimetypes with no apparent pattern.  The list above includes the extensions of the first 10 text mimetypes on my system. 

text/plain files do not have this problem:
test.asc --> test.asc
test.doc --> test.doc
test.txt --> test.txt

unknown extension types don't trigger the problem as far as I have seen:
test.9 --> test.9
test.aaa --> test.aaa
test.y --> test.y
test.jpef --> test.jpef

Other mimetypes are inconsistent:
test.mp3 --> test.mp3.desktop
test.aac --> test.aac
test.tar --> test.tar.desktop
test.rar --> test.rar.desktop
test.jpeg --> test.jpef.desktop
test.emf --> test.emf.desktop
test.pdf --> test.pdf.desktop
test.avi --> test.avi.desktop