By partial channel clipping, I surmise that this happens when the right edge of the bell shaped curve of the histogram of a flat field reaches saturation. Here is a flat field of the green1 channel of my Nikon D3 at ISO 200 approaching saturation (the curve is not exactly bell shaped because of pattern noise). The mean pixel value is 16021, which would correspond to an 8 bit gamma 2.2 value of 252. The minimum pixel value of 15670 corresponds to a pixel value of 251. To guard against partial clipping, one should keep the white balance white point in the low 240s in for an 8 bit gamma 2.2 rendering. Is this what you mean?
Yes, it can be caused by the righthand side of the tail being clipped (with more than 1 pixel), or by unbalanced lighting (causing one channel to clip, using one pixel), but also by a Raw converter. My 1Ds2 got unusably funky at the highest 1/3rd stop clipping point on an earlier version of Capture One, not so on ACR (but ACR sucked for other reasons), probably because it used a more reasonable value assumption for the clipped channel.
Here's an old example of 2 images, one exposed correctly and one overexposed with highlight recovery on:
Adobe CameraRaw V4.3.1:
And on CaptureOne V4.0:
Imagine what would happen if the White Balance had been taken from the 'overexposed' CaptureOne conversion ...
A Babelcolor target included in a scene at the intended exposure + bracketed shots around it would easily show when to back-off, and which exposure level to use/convert, even with a converter that doesn't do it correctly. Of course such an experiment is best done with a studio setup (all variables constant, except exposure).
With the current versions I can use just about any exposure level below 254 8-bit equivalent in all of the R/G/B channels to Whitebalance in a Raw converter and all give the same colortemperature and tint result. It's an easy Raw converter test, just shoot a sequence around clipping, click the Whtebalance, and see when it deviates from the expected values.
The WhiBal usually won't get you as near to the risky levels, so it's much easier to use for White Balancing.