It's one of many patterns that glitches computer. If I did a combo, and end it with a foot sweep (or just simply do a foot sweep), then jumping forward or back would cause the CPU to automatically pop right up and retaliate by jumping towards you. If you hit them at that point, then it is a part of the combo because not seeing them lay on the floor after the foot sweep causes the combo count to continue. On a higher level by doing this glitch, sometimes jumping away will cause CPU pop right up and throw projectiles that is likely guaranteed to hit you because it's a glitch that tells CPU to throw projectiles when the player jumps away, but if you're a teleporter like Scorpion and hit CPU with the TP during the projectile, the hit will count as a combo.
Also, if you hit CPU with Liu Kang's flying kick, CPU will also pop right up, walk forward a few steps, and then uppercuts thin air (This also works with Raiden and MK2 Kung Lao with the Supermans). At the point where they are walking to you, you can get a free hit, and the Flying Kick will count as the first hit of the combo, but at any point you get close, they will throw the uppercut.
When I say "pop right up", I mean you wont even see them rise up, or land on the ground, they just appear as if they were in the middle of something. The Glitch is pretty wacky.