From @ImportanceOfBeingErnest

I just ran the first example from this PR and the result looks like this on screen:

If resizing the figure window with the mouse this can become as bad as

The saved figure is fine though.
(This is with master fetched a few minutes ago, python 3.6.6 on windows 8.1, Qt5Agg)

Let me know if you need further details or want me to test anything particular with my configuration.

Originally posted by @ImportanceOfBeingErnest in #11859 (comment)