Inspired by this thread, I just discovered this old blog entry.:

http://www.os2museum.com/wp/sgdtsidt-fiction-and-reality/

Long story short (for non-techies, I know it is not complete)
"Intel’s 32-bit CPUs always ignored the operand size prefix and stored the full 32 bits
of GDT/IDT base when executing SGDT/SIDT instructions."
Though the official documentation, which emulator writers usually follow, said otherwise;
in simple words, it suggested only 24bits should be saved in a certain situation.
But in a 16/32bit hybrid system, this is like asking for trouble, since the full 32bit base is required here.

I think I noticed a side effect of this several years ago.
In Virtual PC, the latest Win32s wouldn't work without hardware virtualization enabled (haven't tested v1.25).
That's why I did carefully choose the parts for my next PC back then (to make sure it had Intel-VT or AMD-V support just in case).

Anyway, I thought this issue was interesting, so I created this little thread here.