In XFCE 4.10.x dragging a window to any border made it tile along that border.
In XFCE 4.12.2 and 4.12.3 (Only versions tested) Top and bottom do not work.
Dragging any window to the top edge causes it to maximize, instead of tiling horizontally along the top.
Dragging any window to the bottom edge dose nothing at all, instead of tiling horizontally along the top.
The code for this to work appears to be still written to do this in 4.12 but the actions no longer work correctly.
https://git.xfce.org/xfce/xfwm4/tree/src/client.c?id=xfwm4-4.12.3 Line 3255
https://git.xfce.org/xfce/xfwm4/tree/src/client.c Line 3274
https://git.xfce.org/xfce/xfwm4/tree/src/client.c?h=xfce-4.10 Line 3146
Tested on openSuSE 13.2(xfce 4.10) and 42.1(xfce 4.12) on 64Bit.
Yes, this change is on purpose.
You can still tile indows horizontally using the keyboard shortcuts.
Dupe of bug 11779
*** This bug has been marked as a duplicate of bug 11779 ***