Banners are visible through glass pane textures and most/all (not tested) see through blocks like honey blocks and slime blocks.

Gamertags are also covered/blocked by banners.

This doesn't affect gameplay, its more of a graphic bug which was caught by my eye 3 weeks ago and it kept annoying me.

The screenshot up close with the banner is my friend standing behind it showing that their gamertag was blocked by it.

The screenshot with glass is showing how the banner is on top of the glass pane texture despite being behind it.

The screenshot with honey blocks is showing that the banners are 100% see through without any visual effect to make it seem as if it was behind it.