1. All the tags are turned into lower case.
For example, "Window" in <Window></Window> shoud keep its capitalized form; but obviously it was lowered.
2. Error-prone tag closing.
As you can see in the screenshot, the "Grid.RowDefinitions" tag was closed in line 6; so the marked tag in line 24 is redundant, as well as some tags in the same line.
I'm quite sure that the formatting option "WordPress should correct invalidly nested XHTML automatically" in the "Settings->Writing" was unchecked.
And I reviewed my saved post, the content wasn't changed, so I guess the snippet was reformed after read from the DB.