Lockup in jME3 alpha-3 SDK scrolling through shaders

For some reason, jMonkeyEngine locks up when scrolling through some of my shader files in the “Projects” window. I think it is getting hung up on determining which icon to display for them. Most shader files seem to display fine, with a green gear & blue palette(?) icon (or just a blank page). However, when I try to scroll really fast to files to seem to lock things up, they have a small white page with a red ? on it. The whole SDK locks up & becomes unresponsive. I need to force close the application. It always locks up on some specific files…

Can you check for a possible lockup situation when determining shader file icons…? Any other possible explanation?

EDIT: Added the issue here: