A quick tip for something I've found a little frustrating in the past...
When updating the Display Header on a tabular report, the formatting can be different to what's expected. As per below, although I've used capitals in the display headers, the preview and final report replace the capital with lower case.
This only occurs when an 'AS' statement is used within the query which returns the same value as the Display Header.
By either removing the AS statement entirely, or changing the AS statement to something different, the formatting set within the Display Header field will remain.