Dropping brackets on to existing brackets does not save correctly

Steps to reproduce bug
1. Create new score from "Chamber Orchestra" template
2. Drag a thin square bracket onto one of the curly braces
3. File > Save
4. File > Close
5. Reopen file

Expected behavior: The thin square bracket that you added in step 2 above should be present.

Actual behavior: The bracket has reverted back to the original brace.

GIT commit: 93ee3c9

(Operating System: Windows 7)