This is now fixed per:
The non-jittery-ness will be present on all new posts or rebaked posts as we needed to make some internal html changes. (note that the post processor that downloads images must run first which may take a minute or 2)
The non-jittery-ness works fine in all modern browsers (edge,firefox,chrome) but old behavior remains in IE.
It is implemented using serious levels of voodoo and CSS vars described here: