I switched to Modern skin and then MonoBook skin to test out the syntax highlighting feature at IE11.
When I began the line by pressing the space bar, I saw one empty character highlighted. I entered space some more, entered a word, and then pressed Enter. Then the empty characters from one line duplicates into another line. Also, the text cursor starts at the point between the space and the first word.
Nevertheless, when I removed the spaces, entered some words, and hit Enter, the cursor starts at the beginning.
Left image comes from Modern; right, MonoBook.
EDIT: I now realize that the issue extends to other browsers, like Chrome and Firefox, and another skin, Timeless.