There are actually a couple of mistakes with the cat.
1. When you see Blofeld in his office in the volcano, the cat is almost always looking at the camera, regardless of where it is. This causes inconsistency between shots because the cat's head keeps on jumping about.
2. As the cat's head changes position, it also changes where the rest of the cat is. Sometimes it is curled low in Blofeld's lap, sometimes it is layed quite high up across his arm.
3. When Blofeld shoots Osato, you will see his cat jumps from his hands, scared by the loud gunshot sound. It proceeds to curl up between Hans' (Blofeld's bodygaurd's) legs. The scene cuts to Blofeld's face, and then back to the wide angle view. If you look between Hans' feet you will see that there is no cat there.
I know that working with animals is always difficult but I'm sure that they could have prevented these three slipups.
I am also sure that Blofeld's cat didn't run off in the storyline, it was just removed between takes.