Another is https://pl.wikipedia.org/w/index.php?title=Waldemar_Kasta&diff=36944980&oldid=36944831 .

Very strange, looks like metadata is being moved somehow. Do we have any information about what the editors did to provoke this?

(In reply to comment #1)

Another is
https://pl.wikipedia.org/w/index.
php?title=Waldemar_Kasta&diff=36944980&oldid=36944831

Bartosz,

Both these corruptions were by you - were both of them made using Opera? If so, I'm happy to mark this bug out to you (but please clean up after yourself when editing using a blacklisted browser).

Eh, it seems to be Opera-specific after all, I can't reproduce on Firefox (but it reproduces reliably in Opera).

Funnily, my testing shows that the categories are only moved inside the reference if it contains a template. Inserting an empty or text-only reference results in the cateogires eing killed entirely.

function testSpliceBroken() {
var n = 256;
var a = [];
a[n] = 'a';

a.splice( n+1, 0, 'b' );

return a[n] != 'a';
};

This yields 'true' on Opera.

That's probably the bizarrest browser bug I've ever seen, and it seems to be the root cause of this.

Change 72233 had a related patch set uploaded by Matmarex:
Array.prototype.splice polyfill for Opera

https://gerrit.wikimedia.org/r/72233

Change 72233 merged by jenkins-bot:
Array.prototype.splice polyfill for Opera

https://gerrit.wikimedia.org/r/72233

This should be fixed now. Rejoice!

Done and will be deployed tomorrow.