Customizing text in the .properties file of a Plugin .jar file results in the default text being shown

Issue Summary

When editing the .properties file of a plugin to customize text as described in How to edit bundled or system plugins, the customized text does not display.

Environment

Confluence 6.10 and above

Steps to Reproduce

1. Stop Confluence
2. Edit the text in the .properties file within a plugin's .jar file as described in How to edit files in Confluence JAR files
3. Clear the Plugin Cache
4. Clear Browser's cache
5. Restart Confluence

Expected Results

Edit the appropriate text for key entries in the .properties file, see the change in the web UI.

Actual Results

The default text of the key is still shown, the customized text is not.

Notes

This works in Confluence 6.9 and below.

Workaround

This issue can be circumvented by creating a new key in the .properties file and then changing references elsewhere in the plugin to use this key instead of the default key. 

1. Stop Confluence
2. Make a backup copy of the original .jar file
3. Expand the contents of the .jar file
4. Locate the text value you wish to change in the .properties file, notate the name of this key
5. Create a new key with a similar name, adding a ".custom" to the key's name and customize the text
6. Search the contents of the files expanded from the .jar for the original key's name
7. Replace each reference found to the new key name in each of these files, save
8. Recompress the .jar file together with these edited files
9. Copy the customized .jar file back to its original location, overwriting the original
10. Clear the Plugin Cache
11. Clear Browser's cache 
12. Restart Confluence