I note that in the Lazarus 2 install kits, fpc seems to have been renamed fpc-laz, I suggest thats to avoid just this situation. ie, we install the sourceforge fpc, apt sees it and wants to 'upgrade' it to its idea of what we should be using. From memory, it was quite insistent too.
My advice is a very casual user who just wants to have a little play should stick with the Ubuntu packages, mainly because its very easy. Anyone who is even a bit more serious really needs to take charge of their own machine and manually install. Given Martin_Fr recent suggestion that Lazarus 2 might be built with fpc 3.2, especially so. My guess is if you put a sourceforge deb of 3.2 on now, Ubuntu will want to 'upgrade' it to 1.8.4 and in a release or two, maybe the reverse !
Manual install is easy and probably means packages from sourceforge but I prefer to build Lazarus from source rather than have it all end up read only.