1) MaskedEditValidator does not validate Mask in MaskedEditExtender properly for other CurrentThread cultures anymore.
2) BehaviorIDs on controls within UserControls that get used multiple times on a page, duplication issue.
3) Combine scripts not working in ScriptManager.
Ajax Control Toolkit September 2013 Release
1) You can just use the MaskedEditExtender without the MaskEditValidator. The mask should still handle cultures properly as long as you have EnableScriptGlobalization="true" set on your ScriptManager and both CurrentCulture and CurrentUICulture set as well.
2) You can simply delete the BehaviorIDs on those controls used more than once on the page, hopefully you don't need that id client side.
3) Unfortunatly combine scripts must be set to false in ScriptManager for the time being. And yes this will cause more scripts requests and a slower page load time.