I've had similar problems with piper. I tested with 0.5.1-1. With libgtk3-nocsd0 3-1, this program (written in Python) uses CSD regardless.
With libgtk3-nocsd0 git, the problem went away; piper used server-side decorations. Further testing quickly showed that the commit which fixes upstream issue 16 (https://github.com/PCMan/gtk3-nocsd/issues/16) is sufficient.
