Black Bar at Bottom of Screen when changing channels

Sorry to chime in late, but if the black bars bother you, you can press the "EXIT" button anytime a bar is on-screen, and it will disappear. [The button is labeled "Exit to TV" on the remote that came with my new boxes, but my old remote said "EXIT". The position is roughly the same on both -- bottom-left of the OK button, just outside the arrows.]

This works to hide all three bars, btw -- the "info" bar that appears upon tuning, the "preview" bar that shows by using the arrows near the OK button, and the "duration" bar that appears when using transport keys (rewind/FF/pause, etc) or pressing OK while watching TV (with or without "info" bar showing). You can even hide the "duration" bar while FF/rewinding -- handy for "speed-watching" recorded sports or skipping ahead in a program where you need to see the bottom-third to accurately resume playback.

Be warned that if you're watching DVR/OnDemand content, and press "Exit" too late (i.e. fractions of a second before the bar goes away on its own), you might exit your program back to Live TV. No harm done if this happens -- just press "LAST" and you'll be back to your DVR/OnDemand program.

I will also confirm that this behaviour has been present (with some slight tweaks) since day 1 for me...but it seems the OP was convinced of this already. I just wanted to add my experiences, because the black bars are sometimes obnoxious. FWIW, I've had service for over 4 years at two different addresses, with different hardware. Anyway, I think aviewer said it perfectly: 

...it is "invisible" for most channels/shows. It is not until you want to read a banner (e.g. news, stock prices, sports scores) that are covered by it, that it becomes noticably repugnant.

Ours just started this stupid bar on changing channels today... I hate it.. Also added today is the A, B, C buttons (in color) to the guide screen..  I like swapping between two channels with the last button, this pop-up sucks!

@HKr1 - Newer is not always better.

Kill the extra step added to the LAST function - https://forums.att.com/t5/Watching-U-verse-TV/Last-button-now-has-menu/m-p/4954283#M24966

You can kill the black bar at the bottom with the OK button each time it appears.

OK button works quick for coming out of the guide, exit button seems easier when using the last button.. Who thought this browse popup was a good idea i wonder?? You just see all the info in the guide, then it pops up to tell you again, Like Iam stupid!!! < tell me twice 😄  The other stupid thing we noticed is adding time to a recording, goes from old bar format to Dot, then back to bar.... SMH at the people that approve these things.

I first noticed it today.  When I change channels, a TALL black bar appears at the bottom of the screen for EIGHT SECONDS...too long for my taste.  It shows the channel name, the channel number, the name of the program, time of day, time remaining in the program, the and a right arrow labeled "On Next".  That's way too much unwanted information that I can find simply by pressing the Info button.