So, i got some cryptic notifications from UPS and Jason, which I decoded to "I need to brace for contact via support phone line". Got through it. As this is not an enjoyable experience I will share the result to save you the trouble.
My package was held because the precise contents were not stated. I was told to
send a mail to importde@ups.com (the de being the country code for Germany)
stating the exact content.
My suspicion is that the magnet might not be in the content description while showing clearly in xray. Might be something completely different though (e.g. an ambiguous no-value declaration). Anyway, hope this helps..