Are you referring to this recent post in particular?  That is the only report that I have so far seen that claims this.  It is not my personal experience.  I see no mechanism for how the potency would drop, nor did the reported indicate any possible explanation.  Based on my information, I wouldn't classify this as a tested and established fact, more as a single personal report. 

IMHO you should simply perform the different purification stages yourself and try the results of different grades of purification for yourself.  If you can find repeatable results, please report them here, so we can increase and refine our common body of knowledge.