The sequencer made it's own copy of the Markers keymap, which was inconsistent with the rest of Blender, making things confusing to use. I've removed these duplicate keymap entries, and also changed the conflicting hotkeys for Metastrips. Metastrips now use the same hotkeys that their NLA cousins use: Shift-G to add, Alt-G to remove; These were chosen since in user- terms, metastrips are more like "strip groups"