Steps to reproduce:

1. Go to https://cs.wikipedia.org/w/index.php?title=Wikipedista:Martin_Urbanec/P%C3%ADskovi%C5%A1t%C4%9B/3&oldid=17053624
2. Click any section-specific edit source link
3. Make any change
4. Save it

Expected: user is redirected back to the page he edited and informed the edit was saved successfully

Happened: Invalid title error is presented, it says "%C3" is invalid character. The error looks like double URL encoding error, see below:

URL of the page: https://cs.wikipedia.org/wiki/Wikipedista:Martin_Urbanec/P%C3%ADskovi%C5%A1t%C4%9B/3
URL once saved: https://cs.wikipedia.org/wiki/Wikipedista:Martin_Urbanec/P%25C3%25ADskovi%25C5%25A1t%25C4%259B/3#Druh%C3%A1_sekce