I must have misremembered, then; my apologies. Perhaps it was a Win98 vs Win98 SE difference?

Maybe it also required GPU drivers to be installed? I clearly remember the gradient bars.

Win32 GUI wasn't composited until Vista, so it was all GDI 2D primitives rendered directly to the framebuffer. These could be accelerated, but I don't recall any case where some GDI feature would be unavailable if hardware didn't accelerate it - all primitives had software implementations, it just wouldn't be as fast.

However, now that I think about it, such gradient bars must have required at least 16-bit color to work without dithering, so they were probably turned off by default for anything lower. And, at the time, budget video cards had limits on color depth in higher resolutions - e.g. for S3 Trio, if I remember correctly, you got a max of 24-bit color at 800x600, 16-bit at 1024x768, and 8-bit at 1280x1024; you could see the color depth combo box switch as you dragged the resolution slider. So I probably just ran it at 8-bit depth then.

I think they were disabled for 16 color mode, but on 256 colors they were rendered with dithering, which looked kinda cool. I distinctly remember it from playing rollercoaster tycoon; the game ran in 8bpp mode and used the system open/save dialogs.

Given the deep integration of Internet Explorer I wonder if an IE update did it?