The problem can be reproduced with the magnolia demo (http://demopublic.magnolia-cms.com/demo-project.html)

The StageXXL object shows an undesirable behaviour when it comes to the automatic image scaling functionality in connection with the visible "sectioning" of the teaser
items after resizing the browser windows. Sections do overlap the visible container area as shown in the attachments.

Probably, there is something wrong in the javascript routine to calculate the proper image offset
Users and developers are most likely aware of it, but I did not find any information about it. Isn't this a well known problem?