Lx51 "Data Type Different" Warnings ?

Hello.

I have a project that links to a library I created using the C51 toolset.

If I build it using BL51, everything's cool. If I build it with Lx51, I get warnings like this:

*** WARNING L25: DATA TYPES DIFFERENT
    SYMBOL:  _FnName
    MODULE:  .\main.obj (MAIN)

though the application appears to work just fine in the simulator.

If I build the project with source files only (i.e. I compile the modules that are normally in the library, and I don't link to the library) then everything works under BL51 and Lx51.

So, what can I do to enable me to build projects using Lx51 and my libraries, and avoid these "Data Type Different" Warnings?