(In reply to Elitre from comment #0)

See
https://el.wikipedia.org/w/index.
php?title=%CE%A7%CF%81%CE%AE%CF%83%CF%84%CE%B7%CF%82%3AElitre_%28WMF%29%2Fsan
dbox&diff=rEMFR47579045fd3c&oldid=4757901 .
Replace one or more words with "Foobar" (that is, highlight the word(s),
then type Foobar). Works once, works twice, then the third time corruption
happens and le wild snowman appears.
Must say that I only managed to reproduce that in my sandbox, which features
content from
https://el.wikipedia.org/wiki/
%CE%95%CF%80%CE%B9%CF%84%CF%8C%CE%BA%CE%B9%CE%BF , and in this article page.
It happens in Chrome and Firefox, tested under Windows 7, Ubuntu 13.10 and
OS X 10.8.
During an attempt to reproduce, VE also suppressed existing nowiki tags:
https://el.wikipedia.org/w/index.
php?title=%CE%A7%CF%81%CE%AE%CF%83%CF%84%CE%B7%CF%82:P.a.a/
%CF%80%CF%81%CF%8C%CF%87%CE%B5%CE%B9%CF%81%CE%BF&diff=next&oldid=4757859 .

The nowiki tags around the percentage signs were added by me, in an effort to eliminate a possible, if remote, cause of interference.

I found another, smaller, text that manifests this bug https://el.wikipedia.org/w/index.php?title=%CE%A7%CF%81%CE%AE%CF%83%CF%84%CE%B7%CF%82:P.a.a/%CF%80%CF%81%CF%8C%CF%87%CE%B5%CE%B9%CF%81%CE%BF&oldid=4767252

I think the Πηγή template is the issue here; down-page of the template everything breaks, up-page it works. That means it's almost certainly a duplicate of bug 67992.

• This bug has been marked as a duplicate of bug 67992 ***