Now I upgraded xrdp and xorgxrdp to experimental, and the problem still persists:
# dpkg -l | grep xrdp ii xorgxrdp 0.9.2~20170325-1~exp1 amd64 Remote Desktop Protocol (RDP) modules for X.org ii xrdp 0.9.2~20170325-1~exp1 amd64 Remote Desktop Protocol (RDP) server
