I have setup a prefix for class level variables of "_". I found a variable named _TestDirectory which I wanted to rename to _testDirectory
When I hit F6, Resharper had already "suggested" _testDirectory, presumably based on some rules it has for capitalisations of variables. However the Next button was not enabled. I had to manually retype a character to get Next enabled.
I think that if Resharper does not use the "current" value (_TestDirectory) as the starting point in the Rename dialog and changes it, then it should enable the Next button immediately as well. (3.0.504.27)