Board Thread:Bug Reports/@comment-27200931-20170508213228/@comment-27219153-20170511040014

Yes, it is actually moving, as in you have to click where you see it to access the GUI.

Some brief observations.
 * Banners will only move up three vertical blocks with gravel.
 * Protection is still in effect when this occurs.
 * Banners often glitch upwards three blocks when placed one block below the surface. (again, you must click on where you visually see the banner to access the GUI when this happens)

The two 'three's stood out to me and makes me think there could be some sort of connection between the two.