Yes that seems to be a bug, thank you ! I will upload a new version tomorrow, that fixes this issue (and i will also have a look at the other pan_ functions which most likely also suffer from this)!

until then you can replace the pan_setbutton function in the EngFun.cs file with the following pan_setbutton method : http://www.matthias-auer.net/pan_.txt which should enable to pass null as parameter for BMAP in pan_setbutton!

edit:
I will upload the updated wrapper later, as my main pc is currently defect ^^