Unfortunately I'm not able to provide a video, but there seems to be an input bug with Rain. Basically if you do 4-3-D-B quick enough you will actually get 3 attacks randomly picking between the roundhouse or the water-kick. What's really annoying about this is that if your timing is off you might end up getting the wrong special move. I tried recreating the same situation with another char and while I was able to confirm that it's actually possible to do buttons then directions and get a special move coming out, but in no case did I get both the attack and the special. If anyone else is able to recreate this and put it in a video it would be great =)
 
Edit: realized this is something usually called "negative edge", but I still don't think it's supposed to give you 3 attacks by pushing 2 buttons ?

I basically can't ever get Rain to perform Lightning off a simple 3, 3 start-up. Even when the inputs are correct (when you can verify the input accuracy in the training mode), he'll still do the water kick.

Pretty infuriating to be denied that precision for a character that nearly requires exact timing.

I suppose that's the downside of having all moves for a character be either D,F or D,B - while having that mechanic in the game.
Haven't really thought about it, but now you mention it, I realize I've been noticing that too. 

He can't possibly be the only character that has that problem though. 
D,F or D,B seem to be the most common input for specials. 
 
Perhaps no character really should "double up" on inputs for specials.

@EvilDingo: Yeah, you're right. It's not rare for other characters to have this bug to pop up, but Rain's combo's are so dependent on his specials, and he doesn't have a lot of good midscreen striking set-ups, so he seems to get into more trouble than most.

Also, as mentioned earlier, the timing on a lot of his inputs need to be performed excruciatingly quickly--perhaps more than any other character in the game--so this issue hurts him on several fronts.

@EvilDingo: I suppose you're right.

Like you said, then: Bad decision on the developer's part to load Rain up with identical inputs.

Hmm, ye guess my investigation yesterday wasn't thorough enough. Basically what I found yesterday was that any character where I tried to do a combo and then follow it with a special that used the same button as the last hit in the combo (without pushing the button twice) it would come out as either the full combo or replace the last hit with the special. But it seems there are other characters in the game already that will give you both the normal attack and the special. Still doesn't really explain how you sometimes end up with roundhouse though, but after playing with him some more (and reading up on a few tips on how to deal with it) I started getting the hang of it :P It feels really funky though, around half of his specials can be performed in combos just by doing directional inputs.

@Ares42 said:

Hmm, ye guess my investigation yesterday wasn't thorough enough. Basically what I found yesterday was that any character where I tried to do a combo and then follow it with a special that used the same button as the last hit in the combo (without pushing the button twice) it would come out as either the full combo or replace the last hit with the special. But it seems there are other characters in the game already that will give you both the normal attack and the special. Still doesn't really explain how you sometimes end up with roundhouse though, but after playing with him some more (and reading up on a few tips on how to deal with it) I started getting the hang of it :P It feels really funky though, around half of his specials can be performed in combos just by doing directional inputs.

You can also totally cancel the animation of a combo if you input an X-Ray immediately after finishing the combo input, but you'll still deal the damage as though that extra blow had landed.

Some weird stuff happens in this game.