Created attachment 159768 [details]
Python script that displays received parameters in a messge dialogue

The %M parameter introduces additional white space, which means that when passing a parameter like --app=%M, what is actually passed to the command is --app= %M, resulting in the command seeing two parameters rather than one.

Steps to reproduce:
1. Download the attached python script and store it in your local directory
2. Make the script executable (chmod +x showparam.py)
3. Open the Nautilus Actions Configuration GUI
4. Create a new action called "Show parameters" with:
 * Command path: the path to showparam.py
 * Command parameters: --app=%M
5. Save the new action
6. Open Nautilus
7. Right click on any file and select "Show parameters"
8. A message dialogue opens with each parameter the script received on its own line

Expected behaviour
The text in the message dialogue shows one single parameter (one line)

Actual behaviour
The text in the message dialogue shows that two parameters where passed:
 * --app=
 * the full path of the file (%M)