[Rataxes]

A problem I'm familiar with Thuram, though it's often even more irritating in my case. I very often employ the Hit and Run and Hide tactic with Thieves and Rangers, when you're hasted and use the Boots of speed, repeating that procedure can take less than a second. I've noticed that when I backstab someone while hiding, and then very quickly return to the shadows and backstab him again, I'll often go visible on the first swing, regardless of whether it's a real hit or a phantom swing. Waiting a little while before backstabbing again usually cures this little oddity though.

This bug is somewhat fixed by the Baldurash Fixpack, but it's not completely gone.

If you're experiencing this bug only when you're attempting to backstab shortly after you've already hit someone (shortly = less than a round in your case), my advice to you is to wait with the backstab until a whole round has passed. If you hit someone and then try to backstab him, the odds are much higher that you'll stand and lob phantom swings in his direction, than if you wait until your current attack round has passed.