Some mysterious kind of scaler behavior I'm coming up against:

Native monitor resolution is 1280x1024, and that's what fullresolution= is set to.
Trying to scale various video modes within DOSBox to that resolution (with aspect=false), the results aren't very consistent. I've mostly been testing normal2x, but this seems to apply to any and all "2x" scalers equally:

• Emulated mode=320x200 / 320x240: 2x scalers work as expected (so do the 3x ones).
• Emulated mode=640x400 / 640x480: 2x scalers work only if set to "forced". Otherwise, the result is the same as scaler=none. Not sure why, as doubling x and y still fits comfortably inside 1280x1024 without any forcing.
• Emulated mode=640x200: 2x scalers don't work at all (even when "forced") - they show the same as scaler=none. This resolution is "special" in that it is line-doubled to 640x400, but as above, that should still fit when doubled yet again in both dimensions.

Tested in various versions (0.74, mb6, recent svn) - also tried all available output methods, though this doesn't seem relevant to the issue. Always kept aspect correction off, to avoid introducing extra weirdness.
Any ideas?