There's nothing wrong with the way Limewire handles .lwtp files downloaded from Gnutella. But if you download it from the web, you need just to save that downloaded file in your user's Preferences, and click on "View/Appy Theme/Refresh list" to process the new file.
Beware that some web browsers may attach some additional resources to the downloaded file (an icon or application association). LimeWire will ignore the supplementary resources for that file, because it will just process the data fork of that file. However, .LWTP files are in fact zipped files, and if you have some tools that recognize it as a ZIP file (despite of its extension), this tool may alter the content of the ZIP archive to add some files in the zipped archive, or may want to reencode its internal "directory". LimeWire does not name the file with .zip by default on purpose, because there's no guarantee that such external tool will not alter its content in a way that LimeWire will no longer be able to process (for example some unsupported Mac-specific ZIP file extensions stored incorerctly in the data fork instead of the resource fork which LimeWire ignores).

One note: I can just figure out what's happening on Macs according to what is written in the source code. But I have no Mac to test what's happening. Ask to rkapsi instead (if we wants to help) or to a Limewire team member (Sam, Greg and Adam often visit these forums to read comments from users, and sometime take the time to reply; however assurance to get a reply from them will not only made for those that have LimeWire Pro and send their request by email to the support LimeWire address; for LimeWire Basic users, they need to find clues contributed by users visiting these forums and share their experience and ideas).

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