Dev server gives 500 error, production doesn't, uploading gpx traces

I’m developing an uploader for jpstrack and, like a good kid, followed the advice to use the dev server.

After considerable head-bashing, it turns out that, at least for GPX trace uploading, I get a 500 error (with no further explanation) on the dev server, but my trace gets imported when on the production server. Is this a known tech-ops issue?

Server used: vs

URL request used: POST /api/0.6/gpx/create HTTP/1.1

Just changing the hostname (and the password, they are different) is enough to trigger it.