To be accepted for publishing on the Celestia MotherLode, Celestia Addons do have to work in all of the environments where Celestia runs. Is that the problem? Usually the fixes are straight forward but can be time consuming.
The usual problem is that an Addon author has to make sure all the file names are spelled correctly. Windows doesn't care about capitalization, but Linux does. Since Windows is case in-sensitive, both "A.b" and "a.B" are names for the same file. Under Linux, however, file specifications are case sensitive. The names "A.b" and "a.B" specify two completely separate files. As a result, an Addon which specifies the file "A.b" won't find the file named "a.B" and will fail under Linux.