I didn't even know that was a rule, and I use mine a couple times a week. I cook from frozen, too.

Different crock pots seem to have different "rules" but I haven't ever had any problems. When we ate meat I threw it in frozen, and now that fewer kids are at home I don't fill the crock anywhere near half full. (The only booklet I've read said you COULD put chicken in frozen, but even when using second-hand crock pots without their booklets, I've just done whatever seemed to make sense, and it worked out.)

I read somewhere that you can crumple up 3 balls of foil and place them in the bottom to fix this issue. I have only followed this when cooking whole chickens.