This multi device display issue is because it gets corrupt at 14 devices with the old code. The curses display was never designed with people throwing so many devices at it and I never anticipated people would do it. Then I made it stop showing all the devices if there were over 8 - and people complained bitterly, so I made it scale to draw as many devices as you can fit. However pdcurses isnt as smart as ncurses which is used on linux so it just decides to crash instead of display them. SOOOOOOooooo what we're left with is yet another moronic scenario where the choice is either don't display devices and don't crash, or do something to your window before it runs to display them all and not crash, or it will crash. Solution? If you are using LOTS of devices - don't run cgminer with the display enabled by using -T and use a monitoring app to manage that many devices. The basic display was not designed with bucketloads of devices in mind.
Summary: Fuck you windows.
cgminer 2.6.2's display worked very well with 15 devices under Windows. 2.4.1 does not. I don't know if this change was intentional or an accidental side-effect, but it certainly is frustrating to find that something which *used* to work before is suddenly broken without notice.
I have a PC with a 'bucketload' of devices. Under Windows I can conveniently remotely connect to it via Remote Desktop, or VNC, or Live Mesh, or TeamViewer ... I don't use the API because I've no need for it. If cgminer's display remains broken for 'bucketloads' of devices, at least I can run multiple instances. Inefficient and inelegant, but we're not in an aesthetics contest here.
So in the 'grand scheme' of things, it doesn't really matter.