When you move a maximized window - it would always unmaximize. I don’t believe it was ever doing anything else. A maximized window has no borders and if you move it, it is no longer maximized and therefor must be redrawn with borders and what would - by definition - cause the window to be resized, as it otherwise would be larger than the screen, and the best way to handle that is to restore it to the original “unmaximized” size.
If you start by resizing the window to the size of the screen first (by pulling the border to the edge of the screen until they go no further), then maximize it, then moving it will restore it to the “almost maximized” size - is it possible that this is how you remember it working?