FileUploader: Files are replaced rather than added

[brunnerh]

When multiple is set, the existing file list is cleared when new files are selected.
This should not happen, newly selected files should be added to the existing list of files.

See also the demo on the spec page.
(There may be a bug in that version as well: When adding the same file multiple times, it creates multiple entries, but removing one of them removes all instances. Not sure why, maybe the browser tracks file identity and if the items are removed via filter all references get removed. Ideally existing files should not be added multiple times in the first place.)

The same probably applies to FileUploaderDropContainer.

[abradaric]

This is rather major bug for apps that handle files on regular occasion. Any plans to fix in near future?