Supertab shall not be used on my abbreviation settings

Question

I have installed Supertab in vim. Now I face the circumstance that my abbreviations does not work as normal. Which would be: I write the abbreviation atn and it expands to @todo-next. Now I have to hit Tab and Enter, so that the expandation works.

How can I get the iab work as before?

Here an extract of my abbreviations.

# :iab
i atn @todo-next
i ato @todo