ExplorerPane does not fully open

I am adding a bunch of panes to an ExplorerBar (about 48 actually). Initially, all panes' visible property is set to false. Each pane contains four labels. Once the program has finished loading, if I click to AnimateOpen the pane, the pane only partially opens. About 5 seconds later, it flicks fully open.

It's kind of a cryptic problem to explain, but is there any known issue when a lot of panes are added to the ExplorerBar? I have called "FitContents", set "AutoLayoutChildren" to true, etc. I cannot for the life of me figure out why this is. Here's a screenshot.

 

I have discovered that this behavior is due to drawing these controls after they were drawn by a method invoker. Do you have any suggestions how to make these controls totally thread-safe? Am I off my rocker?   

As long as you are doing all your interaction with controls from the UI thread, this should be fine.

Feel free to post a simple reproduction project if you're still experiencing the issue and I'll take a look.