[RTTY] who understands rtty code, strange thing happening, same characters always dropped

[WW3S]

trying to setup a FT-920 with a microkeyer for FSK use with MMTTY....it's not my rig, so not sure the history, it keys up fine, but sends strange or missing characters, tried it with a different microkeyer, and tried it with power all the way down.....here is whats strange, it always drops the same characters, not matter what, I repeated this test several times this morning. It always misses: 
A, C, D, E, F, I, J, K, R and U, and 3, 4, 7, 8, and enter....I suspect the keying circuit in the radio, but not sure, I don't believe anyone else has tried FSK with this rig.....any thoughts?