Kindly refer to the code below. I managed to get this running after my original post to the list and as you can see, I didn't specifically load Zend_Uri_Http. The code below is pretty much lifted straight from the documentation and it didn't specifically suggest the need to load Zend_Uri_Http, otherwise, I would have done this.
The problem seems to arise when I run the code in the context of my preferred framework and so after getting the Zend code to run as shown below, I did escalate the problem to my framework vendor to see whether they could see a reason as to why the code failed in its initial form.
However, I will certainly try your suggestion in the context of my framework and see whether it helps in any way.