Probably a UI issue.
Partial commit is when using the right click menu to commit specific file in Project window. In Project window, right click on the modified file and choose Collaborate -> Publish. This should only commit/push the files selected.

Repro:
1. Download attached project
2. Set up Collaborate for the project:
a. Go to Service window (Ctrl + 0)
b. Choose organization and create a new project.
c. In Service window, click Collaborate
d. Turn on Collab
3. On the top of the Editor, open the Collab menu and try to put in commit message
4. In Project window, right click on a modified file and choose Collaborate -> Publish
5. The Collab menu opens, and try to type in commit message

Expected:
User can put in commit message in the Collab menu.

Repro rate: 3/4 (if it doesn't repro, close the Collab menu and open it again. Or relaunch the Editor with the same project. Sometimes the menu works when using it for the first time.)