Accented characters in exported images getting munged

Question

Lightroom 2.x, OS X 10.5.6, G5, Nikon D80, Raw/NEF/DNG
I'm trying to sort out a problem I'm having that looks similar to other issues with international characters, but is a little different. My problem is specific to keywords.
I don't think this should matter, but I generally import as DNG and never save metadata to XMP. I mainly export to JPEG (to a folder that I zip up) in order to upload photos (outside of Lr) to a sharing site.
What I'm finding is that if I tag my photos (in Lr) with keywords that have accented characters (which I use a fair amount because I often travel to Francophone areas to take photos, and my IPTC data and keywords use correct French spelling) upon upload to any photosharing site I try, the keywords will be munged, duplicated and/or generally messed up. For example, I have a keyword "café". Upon export I can see this correctly in the IPTC Keyword metadata (via a third party EXIF/IPTC viewer, and also using "Get Info" in the Finder). However, as soon as I upload this JPEG to any photo sharing site the photo will end up with a series of keywords applied to it: "caf, cafe, cafã©"
Similarly, a keyword like "naïve" will end up as two keywords: "naã¯ve, nave" I get similar results with HTTP uploaders as well as uploader plugins inside Lr. And so on for è, ô &etc. In the case of Flickr, there will be one "copy" of the keyword that is correct. The others will still be present.
I've read hints that suggest that the IPTC metadata stored in the exported file by Lr might not be Unicode-clean, which causes anything that parses and normalizes select metadata (as all online sharing sites will want to do) to choke. I've heard rumours that the XMP data is properly Unicode clean, but most sharing sites ignore that data, since they are pretty much interested only in EXIF or IPTC metadata (and rightly so, I suppose.)
Is this a defect in the way Lr creates metadata in exported images? Or is is a problem with the way all these sites suck in and normalize the metadata stored in the image? Or is it a subtle interaction between the two that results in incompatibilities?
I haven't tried experimenting with creating or finding a JPEG with no keywords at all and manually inserting IPTC keywords with accents, just to see what Flickr (et al) do upon upload. I've also tried various permutations of the keyword options in the Lr export dialogue with no significant change in behaviour.
I'm interested in who else might be seeing this problem. Is it a Lr only thing, or is it Lr-on-Mac? Or something specific to the two sites I upload photos to?
I should point out that I've been seeing this behaviour since Lr 1.x.

Answer 1

(Jao, AdobeRGB is an experiment. I have a colour managed browser, so I wanted to see if I could tell the difference. This is a test photo from my junk pile.)
I think I see the problem. With something like ExifTool you can see that the keywords are stored in a number of places in the EXIF/IPTC header: Keywords, Subject and Hierarchical Subject. It is the Keywords section that is not Unicode clean, apparently. This is even more apparent if you show the output encoded in HTML entities:
Keywords : Franais, Test Shots, Wings of Paradise Butterfly Conservatory, butterfly, cafŽ, l'h™tel, na•ve, tests
Subject : Français, Test Shots, Wings of Paradise Butterfly Conservatory, butterfly, café, l'hôtel, naïve, tests
Hierarchical Subject : Français, Test Shots|tests, Wings of Paradise Butterfly Conservatory, butterfly, café, l'hôtel, naïve
So, it depends on what section the keywords are taken from. It appears that both Flickr and 23 will try to find the keywords in as many places as possible. This explains the many duplicates I am seeing.
So, now I just have to figure out why Subject is so wrong, and how to correct it (or leave it blank.)