Canon T2i/Bounce Flash Focus Issue

About only explanation that I can think of is if the camera is in Auto mode, it gets to decide whether to use servo or one-shot AF mode.   And somehow putting the flash head to  bounce makes Auto mode prefer servo.

In tracking (Servo) mode, the camera will contiguously refocus while AF is engaged (typically while shutter button is half-pressed).    When shutter is fully pressed, it will take a picture regardless of whether focus is achieved or not.   That is called shutter priority.

Example: just took a picture of something 4 ft away.   Then you point camera at something 10 ft away, and press the shutter all the way down.   Here's what happens for different AF modes:

One-shot: camera acquires focus, and confirms it with a beep and a large round dot lighting up in the viewfinder info bar.   Only after that it will take a picture.   (Focus priority)

AI Servo:  camera begins focusing, but with shutter fully pressed, it takes a picture before focus is achieved.   If you were in burst mode, subsequent shots while you hold the button, would be taken in focus priority.

AI Focus:  camera uses 'gut feeling' to decide between Servo and One-Shot.   This is the mode you get by default when using auto modes.

So, here is a question: when taking a picture, do you press the shutter button all the way, or you half-press and wait for the focusing to complete, then press the rest of the way?    What AF mode do you have set?