Actually, an inverse negabinary would have the same problems. Notice that if you use 9 bits in a regular negabinary system, you get numbers from -170 to 341 -- each time you add a bit, you go from having 1/3 negative numbers and 2/3 positive numbers, to having 2/3 negative numbers and 1/3 positive numbers, and vice versa. An inverse negabinary system would simply reverse which occurs during an odd number of bits and which occurs on an even number of bits.