Uneven meaning the middle of the cigar is more moist than the wrapper.....as the cigar burns, the moisture in the middle creates steam, which expands until the wrapper can't stretch any more and then POP splitting of the wrapper happens.

If they are beginning to unravel while just sitting in your humi, I don't know what would cause that.??? Do you keep them in or out of the cello in your humi? Could some of the cigars just be getting "nicked" up from handling/storage and then splitting when lit?