it seems that the Gallery module (v 0.2.2) and Silverstripe 2.3.0 causes some problems in combination with the [url=http://doc.silverstripe.com/doku.php?id=staticpublisher]static publisher[/url] extension.
What happened was that the page was saved but the site tree in the CMS on the left was not updated. I had to refresh the page to get an up-to-date site tree.
Do I have to enable the static publisher for individual modules or can anyone think of other reasons why this happens? I enabled the static publisher in /mysite/code/Page.php and /mysite/_config.php and I assumed that it would then work for any page including modules.