Tile aggrivation

The tile that went down beautifully quickly developed a stress point in one area of the grout. It seems that a tile was loose, and the vibrations caused the grout to pop out. The tile grew looser and looser because it's right in front of the threshold and you step on it every time you walk through the door. Last night I got back down and cut out the grout and popped the tile out.

Well there's your problem.

Notice how there's only a scant bit of mortar sticking to the edges, and nothing in the middle?
Yea. That's not right. It's also the reason it immediately came loose.
At some point this weekend, I will chisel out all the old mortar, clean up the specifically cut tile, and re-stick it down.