Evolution of 'deign' and 'disdain'

This question just popped into my head yesterday. I guess it might be too basic (or too impossible) for EL&U; but I thought I'd give it a shot.

How come these two words managed to evolve to different spellings? Surely in the days when the grammar nazis ruled the earth with their gimlet eyes and blood-red pens, they should have caught this?

From etymonline.com:

deign - c.1300, from O.Fr. deignier (Mod.Fr. daigner), from L. dignari "to deem worthy or fit" (cf. It. degnare, Sp. deñar), from dignus "worthy" (see dignity).

disdain (v.) late 14c., from O.Fr. desdeignier "disdain, scorn, refuse, repudiate," from des- "do the opposite of" (see dis-) + deignier "treat as worthy" (see deign).

Solution 1:

The author of this blog entry was wondering the very same thing, and came up with this:

Both words come from Latin "dignari", "to judge worthy". The "-gn" of "deign" comes from Old French "deigner", a close successor to "dignari"; its disappearance in "disdain" comes from a newer, Middle English version of the word "deinen", and its offshoot, "disdainen" (when spelling was a lot freer than it is now).