This does look like a bug, or more likely, an incomplete feature.
I guess the expected behavior would be at least the text from the Introduction box is displayed and for bonus points, the entirety of the description as shown in the builder.
In the grand scheme of things though, this is probably pretty low priority, as all of that information is available in the Character Builder when the user has to actually select a background.
I created a new Homebrew Custom Background.
After clicking on it, I saw that there was no information shown except the gained proficiencies.
I copied the Acolyte background: same result.
Custom backgrounds don't seem to show any information on the sidebar.
This does look like a bug, or more likely, an incomplete feature.
I guess the expected behavior would be at least the text from the Introduction box is displayed and for bonus points, the entirety of the description as shown in the builder.
In the grand scheme of things though, this is probably pretty low priority, as all of that information is available in the Character Builder when the user has to actually select a background.
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Just encountered this tonight, so it's still an issue.