You're using phpBB 3.3.0 with flat-style-red for phpBB3.2.2.
If you switch to prosilver, does the problem persist?
Also, I suspect you're using the Italian language pack for 3.2.8 (no 3.3.0 available yet), perhaps something in the 3.3.0 language pack has changed?
Spelling is freeware, which means you can use it for free.
On the other hand, it is not open source, which means you cannot change it or publish it in a modified form.