If I try to create a new text file through Dolphin, I cannot name it <whatever>.txt.  If I try to add the .txt extension, Dolphin will rename the file to <whatever>.txt.desktop.

To repeat:
1. In Dolphin, right-click in an empty part of the file browser pane
2. Select Create New, Text file...
3. Enter filename.txt, and press Enter

Notice that the output is named filename.txt.desktop instead of simply filename.txt.

Some other observactions:
* Using no extension works as expected (eg., filename -> filename)
* Using unknown/unregistered extensions works as expected (eg., filename.bat -> filename.bat)
* Using known/registered extensions triggers the bug (eg., filename.sh -> filename.sh.desktop, filename.jpg -> filename.jpg.desktop, etc.)

This is with KDE 4.8.1.