Wow... split.  I haven't run that command in a long long time.
It has an unitialized variable. add a call to memset after
/sys/src/cmd/split.c:75:

			Resub match[2];
			memset(match, 0, sizeof match);	/* add this line */
			line[Blinelen(b)-1] = 0;

This fixes your example, anyway.

-rob