I have what sounds like the exact same problem as Morna with maybe a little twist. Sorry I don't have any fix to suggest but maybe my added info will shed more light.
(Scavvenjahh, recall my posts in another thread about my Acer V223W monitor's OSD showing 1680x1024 when in fact the screen shots are at 5040x1050.)
Well, when I set up only one or two screens at 1050 the screen image is perfect, i.e., no blurry scaling issues, and the OSD says 1050. But when I go to 3 monitors (5040x1050) it all goes blurry due to scaling of non-native input and the OSD says 1680x1024. This much is just like Morna except my OSD does display 1680 across, not 1280. But, as I learned in the other thread, a screen shot will be 5040x1050.
Now here's the kicker. When I'm in 5040x1050 part of the Windows desktop is pushed off the screen at the bottom. The evidence of this is: In single or double screen mode if I stretch the Taskbar upwards the 10 icons I have in the lower right corner will occupy two rows of 5. See screenshot. Then, if I switch to triple screen the lower row of 5 icons will drop out of site off the bottom.
[img]http://img88.imageshack.us/img88/3051/croppeddesktopqw3.th.jpg" alt="" />[/img]
In triple monitor mode (5040x1050) the bottom icons and the word "Saturday" are not seen and the OSD says 1024. It's like the "missing" 26 rows exist but are pushed off the screen.
:? ???
Edit: For sure it has to be an issue with the 57hz refresh. When the monitors are running in single or double screen all 1050 lines are displayed but the OSD says 60hz.