This is a bug in LimeWire. Your incompletely downloaded file will have this weird name until it if finished, at which point it is renamed. This is an essential component of LimeWire's Smart Resume feature. It is perfectly safe to rename your files as long as they were completed. Otherwise, you won't be able to resume it, and you'll have only a fragment of a file.

For more info on this feature, see question 6-9 of the FAQ.