Simplified, Layman's main job is to make calls to version control utilities. A larger portion of that invocation code has been rewritten: no more os.system(), no more shell interpretation in between. Here's the change log since 1.3.4:

• Handle command line calls "layman" and "layman foo" better. Former now shows a usage summary while latter now reports an error. Both of them kept quiet before.
• Replace os.system() by subprocess.Popen()
• Close stdin of child processes when run in quiet mode to avoid running into infinite and blindly interactive sessions.

Please report bugs for it. Thank you!