switching between editors adds percents to the image width parameter

Example:

• editing in mark up editor - it looks like this:

  !picture.png|thumbnail, align=centre, width=50%!

• i am switching to the richt text editor and back to the mark up editor - it looks like this:

  !picture.png|thumbnail, align=centre, width=50%%!

  ("width=50%%" ???)

• doing it again, an so on - there will be "%%%%%%%"

Viewing the site, is not the problem. - It look fine.
BUT when i export the site with these percents to PDF, the image has only its origin size in the PDF.