What is it with the phoneme "kum" that seems to make it so bloody complicated to spell? On the one hand we have the colloquial spelling "cum" being used in place of "come" in the contexts of orgasm or ejaculate. This is a reasonable example of natural language change, and I don't mind it particularly, if only because of the splendidly smirky double entendre it adds to the mineral discovered in Cummington Massachussets, cummingtonite.
On the other hand, it seems to be increasingly common for people to use the "come" spelling where they mean to use the Latin conjunction, in phrases like "kitchen-cum-dining-room", "wife-cum-manager" or "Horton-cum-Studley". I suppose the vague idea is of a kitchen "becoming" a dining-room, but this introduces an element of process to a construction which should imply apposition alone.
I'm warning you now, if this goes on I may be forced to write a stiffly-worded letter to The Telegraph.