I have an old school Haro BMX bike--one of the first.

I've overhauled it, and have one nagging problem that I can't figure out.

I've installed new brake cable and housing and adjusted the brake so that it stops fine, but the problem is that the cable head keeps popping out of the brake lever (there's only one). I've run the cable/housing length the same as on the original, so it's not the case of too tight. It just pops out. Any ideas?