Unfortunately i haven't gotten into Early Access yet that i may know why the default Print Screen option doesn't take proper screen shots for you.
However, you can try using an external program to take screenshots for you. Give fraps a try.
I use that program for all my screen caps and recording for various games. The free version should take screen shots and do videos up to 30 seconds (with small fraps watermark) for you no problem. Sounds like it will cover what you're after.