Steps to reproduce:

1. Create a Toaster project and build an image (for example, core-image-base)

2. When the build finishes, go to the build dashboard, then click the "core-image-base" link in the left navigation, then select the "Directory structure" tab

3. Click on the right-pointing triangle to the left of the /bin directory: nothing happens

4. Click on 'bin': the directory expands to show its contents and the triangle rotates to point down

5. Click the triangle: the 'bin' directory collapses and the triangle is now again pointing right

6. Click the triangle again: now it does expand the directory (when in step 3 it didn't). 

What happens in steps 5 and 6 is the correct behaviour for the triangle: clicking it should toggle the directory contents. However, for some reason, it doesn't happen unless you click the directory name first.