User blog comment:Kirkburn/Technical Update: July 1, 2015/@comment-3388044-20150704060938/@comment-3388044-20150706103247

“Even with the two different buttons -- mobile vs. desktop -- it should still remember our pull-down choice once made for that session (e.g., desktop vs. desktop xl).”

… should have read …

“Once one has pressed the Desktop button, and selected Desktop XL, it should remember that pull-down selection the next time the Desktop button is pressed during that editing session … just like it used to do from practically the day the CKE/RTE editor was launched until recently.”