PPTP is the legacy Point-to-Point protocol and as such has no concept of modern requirements such as 'Split-tunnelling' nor indeed is concerned about 'DNS leak' prevention etc.
When started, it will expect to be the only protocol in use so will blindly stomp over '/tmp/resolv.conf' with the DNS pushed by its peer.
I have never used 'dnscrypt' so have no idea what it expects to find in '/tmp/resolv.conf', but my script doesn't alter the standard PPTP setup.
NOTE: The only omission that the current published script is guilty of, is in allowing use of the PPTP Client GUI profiles, but I have now modified the script so that a dynamic GUI profile is created to make the delayed start request more user friendly.