https://bugs.winehq.org/show_bug.cgi?id=25703
--- Comment #12 from Vincent Povirk madewokherd@gmail.com --- I can see why WM_PAINT works. It's handled by the builtin edit control which keeps track of text separately.
So the expectation is that the TextBox control only accesses Text once, while creating the handle. It'll be interesting to see what upstream thinks about this.