Losing userdata between requests

[eluser]andrecastelo[/eluser]
Hey guys.

I have a basic problem. I'm building a site where the user goes through a process to configure and set up an order, including an image selection phase, where he had to pick 1+ images. In the last step, I commit that order to the database, but during it, the order is stored in the session userdata. It was working perfectly up until a certain point - when I increased the minimum limit of the images selected to 80.

In each phase I check to see if the order is there, if it has all the elements needed for the step. If it doesn't, it redirects the user to the first step. After I added the limit, I keep getting redirected after adding the images (which is a simple array of strings, the image ids).

What could be the culprit in this case? (removing the image allows me to go through, but the order will have between 80 and 200 images).