The reason that this happens is that the folder tree is being loaded all at once versus loading only the selected folder.
If you experience this issue, or slow load times with the folder tree load when using the resource selector, you will edit the following file in the workarea folder
on line 22: Add PageDepth="1" as shown highlighted in the example below
Without the pagedepth="1" set, the code will be instructed to load the entire tree. Depending on the number of folders in the workarea, loading the folder tree may time out or crash the browser.
With the pagedepth="1" set, the code is instead instructed to load one level at a time via ajax, which will then load the entire content tree without issue.