I have the public beta installed on my rmbp 13" late 2013, and I noticed some weird behavior: I can open applications and access files from my main Yosemite partition. I first noticed this when using spotlight. For example, if I open spotlight and type "system preferences" and open the application, it is not the El Capitan system preferences, but rather my Yosemite version. Similarly, if I try to open, say, Xcode (which I have never installed on my El Capitan partition), I receive a message telling me that my version of Xcode is incompatible with El Capitan and I need to upgrade. Is this normal behavior with partitioned drives? I would think not, but I suppose I could be wrong... For reference, this is a clean install of El Capitan, and did not import settings from a previous install of Yosemite (or anything else). It is in its own 40GB partition, and I have only one other partition, on which Yosemite is installed.