The reports are correct. Build 14901.rs_prerelease 160805-1700 (Redstone 2) fixes all. My Kobo Aura HD hooked up to the PC instantly, showing up in File Manager, Kobo Desktop, and Calibre. Very pleasant.
MS describes this as a small release with improvements to HTML5/Edge. However, my PC did a full upgrade, ending with the "Welcome to the OS" messages. Nothing is mentioned about external partitions being recognized again.
For those interested, this link describes how to force the update (eg if you are not on the Fast ring; also because not everyone on the ring is targeted at the same time). It involves stopping Insider Previews and restarting them.
http://www.windowscentral.com/how-fo...-14901-your-pc