I had this problem with my planet bike front light and a bontrager computer. Interestingly when I got a cygolite 420 there was no problem and I could move them closer. My guess is there's a bit of luck whether a light leaks the right kind of interference in the right spot. I don't know if it helps you, but my problem was only when blinking. Solid lights didn't cause a problem.

Before I upgraded I experimented till I found a spot where they were just far enough a part they would both work. It wasn't ideal position, but at least they worked.