This is more of a tracking bug than anything else, but it should be something people are aware of and something that's formally logged; the VisualEditor is very slow on large articles, to the point where it causes confusing output.
Using the example of https://en.wikipedia.org/wiki/OpenOffice - I edited this and it took a good 20 seconds just to render 'review changes', and another 20 to save. David Gerard did the same and the server popped up "Error saving data to server: timeout." with both 'review' and 'save'. Despite this, it saved anyway.
Obviously as a long-term thing: we shouldn't have an editor so slow that someone in an industrialised, Western nation (i.e. the UK) can't make things work. As a short-term thing, we shouldn't be informing users "something has gone terribly, terribly wrong, abort!" when it has actually saved.
 It's David Gerard, he's not going to be using dial-up.