Problem with Vietnamese unikey in Leopard x86 10.5.5

[hoangbv15]

I'm running iATKOS v5i, everything including networking, audio, graphics is working like a charm. But one small but annoying problem.
I'm using Vietnamese unikey preinstalled in Leopard, Simple TELEX mode, and all of my keys except for "d" are normal. I always have to tap "d" 2 times for it to appear. In U.S. typing mode, "d" is just normal, but it seems to be allergic to Vietnamese unikey.
Can anybody help?