Hi, Alessandra,
well, it's obvious, if you - and I - think about it.
The plugin is called "hideEmptyColumns". Even if the text {Q1_SQ001...} is empty, there is still the tag. So the column is NOT empty.
Okay, probably you can center the text by css.
Either insert into the question text (in source code mode)
Code:
<style type="text/css">
th.answertext {
text-align:center !important;
}
</style>
or if you want to use it generally add it to the end of "template.css" without the <style> tafgs
Best regards
Joffm