Some neo-Indo-Aryan languages sound unusual to us because they are not our native tongue and very “discordant” with respect to saMskR^ita. Hence, those “funny” words sort of make us sit up and try to figure out their evolutionary paths. Today we were amused by some reminiscences of usages in marAThi that was spoken in the land of our youth. This led us to some peculiarities in sound changes as this branch of Indo-Aryan, which probably included marAThI, gujarAtI and ko~NkaNI diverged from its ancestor.
Thus even as marAThi and gujarAti-s ancestors broke off from the more northern radiations there was an unusual kSh>s transition, with his change apparently happening to a greater degree to the South i.e. in marAThi.
Now a semantic question why does saMskR^ita kShaNa give rise to saN/khan which means a festival while the former means a moment or instant. Apparently there are rare instances (even the notorious MW dictionary lists some) where kShaNa is used for a festival in saMskR^ita. Given that festivals were marked by the instant or moment of the moon entering a certain nakShatra or attaining a certain tithi or the holy muhUrta, it appears that word kShaNa in a calendrical sense became equated with festival in this southern Indo-Aryan branch.