Having same problem here:
I’m using two machines: Win7 64 bits and Win 8 64 bits.
Both machines using WordPress 3.6 Multisite in Brazilian Portuguese.
XAMPP version: 3.2.1 compiled in May 7th 2013.
The problem is the same in Chrome (Version 29.0.1547.57 m), Firefox (21.0).
Here is a print screen: https://www.hericdehon.com.br/nextgen.jpg