files get mapped (assosciated) to programs, and the operating system keeps track of what program to use when opening a file. When more than one program is used to open a file (like a .jpg or .mp3), the file assosciations can vary.

So the problem you note isn't really a LimeWire problem, but normal system behaviour.

See your Operating System's help for "file mapping" or "file assosciation" or maybe the term to use will be "Open with."