Don,
I have used both Lenox and Stonhenge with VDB without the staining you describe. In fact, the only thing that you do that is a bit outside of my procedures with VDB is the very long wash in citric acid and running water, 10 minutes in each if I understand your correctly. I usually add a bit of vinegar or dilute acetic acid to the first wash/development, but limit wash time to no more than 3-4 minutes. My first inclination was that you did not wash/develop long enought, but on second thought maybe there is something in your water at this time of year that, in combination with the long wash, leeches into the paper and contributes to the stain.
So perhaps you could work backward. Just develop the print for 2-3 minutes in a tray of distilled water to which you add a few ml of vingegar or dilute acetic acid, then tone, fix and evaluate the results.
Sandy