When I use Pick Block on any colour banner, it gives me a Black Banner on Creative. On Survival if I place one and have the same type in my hotbar it does not jump to it like it normally should do. But in Survival it does jump to a black one regardless of the colour of the one placed down.

Pick Block normally gives the exact colour item you Pick Block on (Creative) or selects it for you (Survival)
It has not happened on any other block with multiple colours/types I have tried.

To trigger the bug:

1. Be on Creative or Survival (but if you are on survival make sure you have 2 same colour banners)
2. Find out how to use your Pick Block function (Default is Button 3)
3. Place any type of banner but not a black banner.
4 Try to Pick Block on it
5. Try to Pick Block on your banner, it will either give you a black banner or it will not switch to the same colour one in your hotbar.
6. For an extra test you can do on Survival. Place down any colour banner (not black) and make sure you have a same colour banner as you placed down and a black banner in your hotbar. Then Pick Block on the banner. It will go to the Black one!

UPDATE!
Using Control + Pick Block will give you the correct colour one! (NBT)