As title says, borderless makes the window frame invisible, but still reserves the height and width and this can't be changed with borderlessX or Y.
Apparently you need to restart the game for borderless to take effect properly.
gfx_restart doesn't cut it
still an issue. even with gfx_borderless 1 in an autoexec. gfx_restart and restart of game fixed it.
the game then ran at very low fps untill i hid my start-menu, which was "Always on top" and shown on top of game