My opinion is that the grain masking you get with proportional stain is a very good thing because it is a stain clustered around the silver particles. General stain is garbage because it does absolutely nothing to enhance print values, and may in fact detract from them by limiting the contrast range of the negative. Often you can just print through general or base stain, but when using high speed films like Ilford HP4+ in very flat lightiing situations the stain may actually prevent you from getting enough contrast. This is because there is a finite CI to which a film can be developed and the log value of general or base will subtract from that value one to one.
However, it is perfectly natural to get a fogged rebate with outdated films or with films that have been prematurly fogged by heat, even when usisng staining developers that produce only proportional stain. The stain reacts proprtionally to the built-in fog just as if the high b+f level had been created by light.
There is really nothing you can do to eliminate staining of the rebate with outdated film but you surely should follow David Goldfarb's advice and avoid the alkali afterbath. I personally think the alkali afterbath is very bad practice even with fresh films but at least with films that have a low b+f to begin with the afterbath does not do a great deal of hard. And that is about the best thing I will say about the afterbath.