When committing a file, SourceTree will have a popup dialog for Uncommitted Submodule if the file in Submodule has been modified. Clicking the commit button in this popup dialog will show uncommitted files in Submodule.

Somehow SourceTree have this popup dialog even though the file in Submodule is not modified. Clicking the commit button will show "Nothing to commit" message and there is no way to cancel it.

SourceTree should have a button to cancel committing submodule to close the popup dialog.