Added '-' to invalid tag characters because it causes problems.

boards/forms.py

@@ -38,7 +38,7 b' class PostForm(forms.Form):'
 
 
 class ThreadForm(PostForm):
-    INVALID_TAG_CHARACTERS = ['+', '/', '&', '=', '?']
+    INVALID_TAG_CHARACTERS = ['+', '/', '&', '=', '?', '-']
 
     tags = forms.CharField(max_length=100)