That "disappearing" happened to me too back when I hexedited animdata.d2 to force-match the framecount for monsters. I don't know what was causing it.
The solution for me was edit every new animation, so that the framecount of the animation matched the framecount of the animation I was going to replace. This way you don't have to deal with cofs nor with hexediting. It's a boring process, but it works to the best of my knowledge 
And about all the weird things you're seeing with the dragon, that's because you have to adjust the dragon's offsets. When you save a dcc file, see in that screen where you select the number of directions of your animation? In this screen you can also edit the dcc's offsets. Adjusting offsets is a LONG, BORING process, but necessary.
A little example:
So you're in the game and you see your dragon walking towards your character (for example he is displaying his downright animation). However, you notice the dragon is misplaced on screen, it looks like the dragon's downrigth animation is displayed to the left of where it was supposed to be.
Well, this means that you have to re-save your dcc file, and in the offset-adjust screen you have to increase the X offset for the direction number 4 (the downright direction) 
The offsets work this way. Every animation direction will have a pair (X,Y) of numbers (this direction's X and Y offsets). It works just like a cartesian coordinate plane (with the X and Y axis). The only difference is that an usual cartesian plane is like (hope this looks ok on the post):
(Y)
+
^
|
|
|
|
(0,0)------------>+ (X)
while the offset plane is like
(0,0)------------>+ (X)
|
|
|
|
|
v
+
(Y)
So a negative Y offset means the animation is displaced UP, and not down.
Well, all this was just to say:
- If an animation's direction displays to the left of where it was supposed to be, increase that direction's X offset.
- If an animation's direction displays to the right of where it was supposed to be, decrease that direction's X offset.
- If an animation's direction displays up of where it was supposed to be, increase that direction's Y offset.
- If an animation's direction displays down of where it was supposed to be, decrease that direction's Y offset.
Of course you'll need to combine a lot of those if your animation's offsets are completely messed up 
Hope this is not too confusing...
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"Get me a balrog attack-1 hand-to-hand animation, and I want it yesterday, the paladin is almost here!" ---> DMA1HTH @ offset 0006A480h. - Myhrginoc