Edit a page with VisualEditor and paste following wikitext: this [[is]] wikitext (including leading space).

This actually produces \n this [[is]] wikitext\n (which will be parsed as a <pre> tag), whereas I only expect this [[is]] wikitext (which would be parsed as <pre> tag only if this has been pasted at the beginning of the line).

In fact, at home, that depends on the copied wikitext origin: I can reproduce this issue when I copy wikitext from Firefox URL-bar, but if I copy wikitext from my local text editor, then pasting just removes the leading space (this strange inconsistency may come from my local OS).