Lightroom: What is the color space used for high-quality previews?

Question: What is the color space / gamut used by the lightroom previews in quality "high"? Is it AdobeRGB or ProphotoRGB?

The manual states "The Library module stores Low and Medium quality previews in the Adobe RGB color space, and High quality previews in ProPhoto RGB."

However, various web sources, and Victoria Bamptons LR FAQ, state that Adobe RGB is always used for previews.

A simple experiment when I set my monitor profile to ProPhoto and imported a ProPhoto images with maximum saturated colors into LR leads to the same conclusion: The previews in library module always seem use Adobe RGB with quality setting "high" - they appear less saturated then the develop module.

Ist the manual wrong?

P.S. I know that for "normal" wide-gamut monitors with AdobeRGB-like gamuts, this is irrelevant. However, it would be good to know when using monitors that exceed AdobeRGB at some colors.