I'll throw out one more theory about XTOL that I haven't yet seen in this thread. XTOL can be pretty sensitive to the water you use when mixing and diluting your developer. I've only been using it for about a dozen rolls, all of them mixed and diluted (1:3) using distilled water for purity, so I can't report the effects of bad water from my own experience, I just know it's caused other people problems. Tap water often contains a mystery mix of trace chemicals that can unexpectedly interact with XTOL. From all the reading I could do on the web and my own limited experience, if you stick with distilled water and are sure you have adequate developer per roll, perhaps a bit extra to be safe when diluting 1:3, you'll be fine. Reticulation is a possibility, but I have yet to see it actually happen myself regardless of temperature shifts in the final wash. However, I may have to experiment now to be sure. ;-)