Capacitive button lights blink if locked while looking at PowerPoint presentation

[zinrai]

If I go into the Office app, press on Explore PowerPoint, wait for the presentation to load, and lock the phone, then the capacitive buttons blink until I unlock the phone again. This happens with every single PowerPoint presentation, not just the one in the Office app.

Is this a Lumia 900 issue, a Windows 7.8 issue, or a personal issue?