Note the Restore Defaults button is fairly close to the OK button. This
will snap the values back to the default, particularly if you're careless swiping over it with a tablet pen on the way to the OK button instead of a mouse click directly on the button.
Ooh, good point Rhoel - the page at
http://www.e-frontier.com/go/animestudio/compare says Anime Studio (standard version) has a limitation of a maximum 768x768, unlike the Pro version which has a maximum of 9000x9000.
Also, I doubt this is the problem (which I've never seen before), but just thought I'd mention it:
Changing the project settings has no effect on the workspace size, only on render size.
You can have a project setting of 4000x3000 and a workspace view of 320x240, or vice versa (umm, assuming you could display a window that size).
So changing the project setting will have no affect on the workspace view after you click OK, assuming you haven't changed the actual ratio of width to height.
Note also you can't modify the preset sizes. Typing in your own values only changes the current project settings - you can't type in new values and click the presets button to save. I really don't think you did this, but I thought saving new presets was worth trying at least once

.
Regards, Myles.