In a recent discussion with eNjoy (yep, there should be some media player and I'm hoping it will be usable soon) developer, I found that Ubuntu does not installs FLTK correctly or at least packager missed few important things.

FLTK keeps header names under .H extension; I'm not sure why is this, maybe legacy stuff or due some strange platforms that likes C++ header files ending with .H and source files ending with .C (FLTK uses .cxx here). And since everyone expects .h extension for headers no matter used C or C++, FLTK plays fair here too: installation procedure will create .h symbolic links to those .H files (I'm aware of attempt from C++ purists to keep C++ headers under .hpp extension or no extension at all, like headers from STL, but I'm finding this practice little bit disgusting).

Now, as you guessed, I used .h for FLTK normally as for any other header file all over the code (edelib and ede 2.0), not thinking that some packager will mess things up. Maybe they see this as perfectly normal, but shouldn't distro package resemble the state " make install" or whatever created?

So, latest revisions of edelib and ede2 modules have fixed this " issue". Hopefully, things are less distro dependent now, but, as usually, you never know...