Why does the Fujifilm X30 limit shutter speed limit in aperture priority mode?

According to FujiFilm X30 specs:

Shutter speed: (Auto mode) 1/4 sec. to 1/4000* sec. , (All other modes) 30 sec. to 1/4000* sec. * 1/4000sec. at small aperture, 1/1000sec. at full aperture

In reality, when using Aperture-priority mode and a low f-Number (e.g. 2.0), the shutter speed goes up to 1/1000 while making overexposed pictures if there's too much light. (The shutter speed value turns to red.)

In Manual mode with f=2.0, the indicator turns red at 1/1000s but allows me to continue up to 1/4000s.

If the camera is capable of taking a picture at f=2.0/ss=1/4000s why doesn't it allow to do so in the Aperture-preference mode?

Answer

This is actually a characteristic of the leaf shutter used in Fuji's X10/X20/X30 and X100 cameras. The leaf shutter can only travel so quickly. The wider the aperture is open, the slower the shutter speed has to be to accommodate the operation speed of the leaf shutter. It's a mechanical limit.

In M and shutter priority modes, Fuji is allowing the faster shutter speeds with only a partially opened aperture anyway, but at the detriment to background blur (the bokeh becomes choppier) and accuracy of exposure. Dpreview's detailed review on the X100 shows this effect very clearly. Because most people use aperture priority to control DoF and probably to gain a smoother background blur, chances are good Fuji decided to limit the shutter speed farther to mitigate the effect on the bokeh, while still granting access to the faster shutter speeds in Manual (where any camera lets you shoot yourself in the foot all you want) and shutter priority, where it's safe to assume that the shooter prizes a faster shutter speed more than the quality of the bokeh, but they warn you about the exposure issue.