Do you have this setting in Web.config or user.config with a setting other than h2?
<add key="ModuleTitleTag" value="h2"/>
like do you have this with an empty space?:
<add key="ModuleTitleTag" value=" "/>
that would cause it.
there is a new feature that allows you to control the heading tag used and even edit it, but it uses the default from the above setting when creating new instances.
If you add this to user.config
<add key="EnableEditingModuleTitleElement" value="true" />
then you can edit the heading tag from ModuleSettings.aspx ie click "settings" and look on the General tab