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 ⏎. 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 ⏎, 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.