The textarea jumps around while the Visual Editor is loading. Looks like it shrinks to zero height and then expands again to the final height. But this is annoying...
Related Gerrit Patches:
|mediawiki/extensions/Flow : master||Cleanup use of min-height to prevent vertical height flicker|
This seems to happen because resource handling in prod is so much faster than our development machines were. Can look into how to make this nicer with fast loads, but still provide a reasonable experience when resources load slower.