https://bugs.winehq.org/show_bug.cgi?id=28141
--- Comment #7 from Vincent Povirk madewokherd@gmail.com --- I tried it with the data source from https://sourceforge.net/projects/twain-samples on Windows, and it worked. Unlike our data source, this one sends MSG_XFERREADY through the DSM, not using the window passed to ENABLEDS.
That's probably what we should do, but I need to figure out a way to test that.