I'm the creator of the Sanguino, and I'd like to clarify a few things:
by 'compatible with arduino', we mean that the Sanguino is:
* programmable with the Arduino software
* implements all of the core arduino functionality (ie: everything on http://arduino.cc/en/Reference/HomePage
it's my goal to keep the Sanguino as compatible as possible with non-official Arduino libraries, but as you may imagine it is quite a bit of work to ensure that they all stay synchronized. i'll try to make a note of this on the sanguino website to avoid confusion.
the reason for creating the sanguino, as well as my day to day work is hacking on RepRap, which keeps me really busy. i'll try and dig into the library code that is having a problem here and try to figure stuff out, but it may take me a little bit to get up to speed with the library and figure out whats wrong.
in the meantime, i'm sending mem a Sanguino kit in hopes that the creator of the library will be able to easily spot and fix the problem.
unfortunately, with low level hardware access happening, you tend to lose compatibility between different microcontrollers. all of the pin to port mappings are published: you can either check out the schematic or look at the code in the sanguino 'core' folder. Both are freely available.
good luck with the LCD, and I hope we get this fixed asap.