Here is a link to the projectarchive. https://www.dropbox.com/s/7507oxl5m72nat9/Proptest1_1-30-15.projectarchive?dl=0
Its 22MB. Not sure what your posting limits are. Tried to add it to the post but it dumped it.
Basically, what happens is that it will compile, and go online, and work just fine. When I go to add another device, say a Modbus or SPI device, it will remove the Fixstuff library, and subsequently not recognize the propi2c device and use in the code.
If I re-add the library, save it and exit and restart Codesys, I have both my library, and the new one, and it works fine.
Its very repeatable, which leads me to think its either something I have done wrong in say the device config file, or its a bug.