Issue Title: On saving file, different data are altered leading to many minor file changes.
Environment: Windows 10 Home, StartUML v5.1
1. Open a model with some schematics/models.
2. Add a new schematic, or modify one of the available schematic for a bit.
3. Save the file
Expected Result: The stored .mdj file should only have changes on the components you added/modified. That way you can track at a high level from the git-difference the most changes (components additions/removals, changes etc).
Actual Results: The stored .mdj contains hundreds of minor modification in numbers, on components that you didn't even touch. This makes it impossible to review the git-differences on the file.
Thus when you are using the .mdj file with git, it's impossible to see the actual differences of the text .mdj file, thus to get a better versioning understanding. As an example I'm showing the generated differences on components I didn't touch, among two version of the .mdj file. The numbers of the components are modified without reason, and this lead to a git diff, with hundreds of changes especially if the model file contains more many items (I'm getting ~1000+ such differences in every saving I do in a file with multiple schematics). This seems most like a Bug, with affect negatively the text/git-versioning of the models.