Hi Mick, good to hear that thus far you managed to get rid of the pop-up warnings.
In my case unfortunately there was no reliable fix. Neither with the .Net4 upgrade, nor with switching on the caching, using the default temp folder, or disabling my wife's account on my computer. At best the pop-up appeared only after tweaking the second or third control point instead of more or less straight away (there is no real consistency in the behavior, it also depends how much you tweak a control point).
I didn't check if using numerical values would help, but I guess it helps as with using the slider Capture immediately seems to start recalculating. In general I believe the hassle is when Capture needs to recalculate all edits and then exceeding some thresholds in what it can read/write to temp/disk.
The only true workaround is to switch off the keeping edit steps alive when editing in the general preferences tab (don't know the English translation reads). But this is too much of a compromise for me - I then prefer to wait a bit longer using 2.2.8 (and for 2.3.1).
If you like you could do some testing with b/w conversion. First do your RAW processing (sharpening and contrast on 0, some shadows and exposure), then add 3 or 4 color points. Then a high-pass filter applied locally to strengthen some contrast. Then b/w conversion, playing with the filter. Then tweak your color points. Then add two locally applied levels & curves for locally increasing contrast (you may want to play with multiply blending mode). Then sharpening and finally add some grain or duotone. At the end you tweak both the color points and the amount of high-pass filtering again. Then close the image, open it again and tweak these color points and filtering again. This should give Capture the shivers. At least in my case.