Hi!
Wikidata seems to use the experimental Java server, not the default and more tested Node.js server.
Yes, it is built on top of Java ldf server, since it integrates with Blazegraph which is of course Java.
I reported it here: https://github.com/LinkedDataFragments/Server.Java/issues/41
Thank you, ans thank you for responding so quickly! I'll keep an eye on it and will report any oddities.