TextBox selection behaves weirdly when changing via Current

[frenzibyte]

Easiest example is a control point popover in osu! editor (with ppy/osu#18220), which has a textbox-slider component bound to one current bindable, and when the textbox has selection in it, results in the following issue:

CleanShot_2022-05-11_at_11.13.59.mp4.mov

It's expected at that point to clear selection, rather than keeping it or halfing it weirdly as shown in the video.