Bob, I'm not Victoria, but I also am running Windows 7x64 bit, with CS5 (specifically version 12.0.4), and have the 6.7RC installed (not sure what CS5.1 is and if different?). I also do not get prompted. I used to get prompted. Thinking it was 32 v 64 I tried both. Incidentally, Victoria helped me elsewhere govern which Photoshop version is launced in the "Edit in CS5". You do it in the registry at HTLM\Software\Microsoft\Windows\CurrentVersion\App Paths\Photoshop.exe . There are two keys (Default) and Path, change them as follows (path of course leave off the file name):
32: C:\Program Files (x86)\Adobe\Adobe Photoshop CS5\Photoshop.exe
64: C:\Program Files\Adobe\Adobe Photoshop CS5 (64 Bit)\Photoshop.exe
But I tried "reset all warnings" and still do not get prompted.
The good news is that it appears to be accepting all the edits from Lightroom, and is getting it through ACR (you can tell because once in CS5 it shows .NEF not .TIF as the file type).
It also does prompt when I set it up as an external editor (which I think is normal).
The bad news is now that you called my attention to it, the images do not look the same. Below is a screen shot with both panes shown at the same time, and it's subtle, but the image from photoshop is brighter, notice in particular the chairs over the batt, and the white haze on the batter's left knee.
I tried taking some images and making extreme adjustments to see if Photoshop was missing something entirely, like a new 2012 process slider, with no luck. Any extreme setting showed up in CS5.
I also checked and soft proofing was off in both, and preserve profile was set in CS5 so I don't think it is a profile issue, and I tried both the library display and develop display in photoshop (with soft proofing off). CS5 is consistently showing a signficantly different appearance (basically brighter) than LR.
Now I am confused. Shouldn't these two displays be identical?