YouTRACK "IntelliJ IDEA: Backlog (IDEABKL)" vs "IntelliJ IDEA (IDEA)"

I have a quick question regarding the IDEA issue tracker: What's the difference between "IntelliJ IDEA (IDEA)" and "IntelliJ IDEA: Backlog (IDEABKL)"?

That's http://youtrack.jetbrains.com/issues/IDEA vs http://youtrack.jetbrains.com/issues/IDEABKL

I think this question was asked back in 2007, but received no answer then either (http://devnet.jetbrains.com/message/5202406).

I'd really appreciate some official clarification from the IntelliJ team.