When upgrading OpenNMS, it is important to clear all the browser cache prior start using the WebUI against the upgraded version.

This is important specially for those pages where JavaScript is heavily used like AngularJS applications (for example, the Requisitions UI).

Bower, which is the library used to manage JS dependencies, always put the link to .js and .css of the dependencies on the same place, so if you upgrade a dependency, your .jsp/.htm file doesn't require changes. I think this confuses browsers somehow and generate undesired results when rendering the pages.

For this reason it is important to add a note for this on the "How to upgrade guide" (thanks for the tip).