We are using the latest version of K2 on a joomla 3.1.5 website and when the k2 item launches the image appears to float over the text.

Any hints on how to fix this?

The template you are you using is not compatible with Joomla!'s default lightbox.

You should remove the modal class from your overrides(item.php). You can replace the link with Bootstrap's lightbox link or completely remove it.

You could also check this topic
getk2.org/community/New-to-K2-Ask-here-f...422-item-image-issue
if you wish to make this change to your template's bootstrap.css file.