Importing passwords into Vault opened a panel that was only as large as the item list it covered. On a Vault with a few items - or a new one with none at all - that panel collapsed to a few hundred pixels, and the list of items found in your file scrolled inside it, giving you a scrollbar within a scrollbar in a box that used a fraction of the window.
Import is now a screen of its own, like opening an item. It takes the full width of the page, the list of found items runs down the page rather than inside a capped box, and you leave it through the "Vault" link in the page bar or the Cancel button.
Going back and picking the same file again now works too; previously the file had to be changed before the import would re-read it.
Nothing about how import handles your file has changed: it is still read and parsed entirely in your own browser, and each item is encrypted there before anything is sent to Magpie.