Editing Sandbox page in WYSIWYG creates too many changes in the diff

I edited the sandbox page in WYSIWYG and just modified some text (see screenshot).

I was surprised to see so many changes in the diff that shouldn't be there:

• Table changes that are not clear (the change look similar to what was there). Why is the default not canonical?
• Attachment size metadata updated

Note: This issue will probably need to be translated into several other issues when we discover the problems.