Oh wow. I really have to hang my head in shame.
Under my user settings the option ‘disable visual editor when writing’ was selected.
Doesn’t look like there is a problem after all!
I’ve just set up a new installation of WP 3.8 with exactly the same theme and plugin setup and the WYSIWYG is working fine.
I’ll stick with this 3.8 installation for now, but there is obviously an issue to be resolved for v4.
That second plugin should of course be
Advanced Custom Fields Repeater – 1.1.1
I’m a very happy punter, but unfortunately I have the same issue as described above – a general slow down that gets worse the more times the repeater (with conditionals embedded) is repeated.
The fix above has improved the situation a little, but there is certainly some very substantial (and probably unnecessary) JS overhead going on.
Looking forward to the official fix.
T