Filing this for a colleague. Repros in nightly.
Details in this example:
This works correctly in Chrome.
The current behavior is compatible with the Cocoa text system (you can use the TextEdit app on OS X to see this).
The current behavior on iOS and OS X are by design to be consistent with our other text input systems. If you are encountering this problem on Gtk or another port, and this violates the expected platform behavior, please re-open the bug with relevant comments.