I'm going to take a crack and say it's a problem during coating. I've talked about this in other threads, but to sum it up, you're not getting th VBD solution into the fibers of the paper, but rather it's getting trapped in the surface sizing of the paper. When you wash the print, the surface sizing liquifies and allows the image to bleed.
Try a simple test: Coat your paper with distilled water, about the same amount you'd use to coat your image, or a 25% more if you want to be certain. Allow the paper to dry completely and then coat the VBD solution. Expose and process as normal. I'd bet you don't see any more bleeding after that. The distilled water has broken down the sizing and has swelled the fibers of the paper so they accept the coating solution more easily.
The surface sizing has homogenized with the pulp sizing in the paper and will no longer reticulate or expand causing bleeding.
Thanks for reading.