WYSIWYG "breaks" pages

The WYSIWYG Editor breaks a wiki page in a strange way. Not only does the code formatting look different, but also the resulting page.

Create the following text using the wiki editor:

One word

{highlight}highlighted{highlight}

. Then a new line:
One word

{strike}with a red strike{strike}

.

Have a look at the preview. Then switch to the WYSIWYG editor and the back to preview. You will note that the result looks different.
I have attached two screenshots of the result.

Now swich back to the wiki editor. The code looks now completely different:

One word

{highlight}highlighted{highlight}

. Then a new line:
One word

{strike}with a red strike{strike}

.