Occasionally, I encounter problems while editing in the sourcetext. My cursor would be on one line, but the edits would take effect elsewhere in the text (usually the line above/below). I attached a screenshot, where the cursor is visible, and the two opening accolades ("{{") are on the line below.
I'm using Chrome on mac, have a number of extensions active, but never encountered this until I activated the new wikitext editor in the beta functions.