Why not hydrochloric (or acetic) instead of oxalic?
Gattu, oxalic acid and calcium carbonate buffer will neutralize to calcium oxalate which is insoluble, therefore won't wash out. Yes, the paper will be neutralized indeed, but the neutralization product will remain in the paper.
I just don't get why comparingly harder to obtain and more expensive oxalic acid (which the neutralizing product - calcium oxalate - stays in paper and gives a gritty surface, depending on how heavy was the buffer) is used for the purpose of neutralizing buffered paper, whereas easily obtainable and cheaper hydrochloric acid does the job (and that's with the added bonus: its neutralizing product - calcium chloride - is very soluble in water; it won't be there - unlike calcium oxalate - after the rinse!)... Maybe there's something about longevity (oxalic being better in terms of the keeping properties of the paper), but I couldn't find any info/comment/reference about this. I also absolutely couldn't find a reason why oxalic acid was chosen instead of hydrochloric acid? (Maybe because pt/pd printers are more likely to have oxalic on hands, since it's used to facilitate dissolution of ferric oxalate and/or to mix developer from raw materials and/or it's just safer to deal with oxalic acid -> but then there's acetic acid which also is safer to handle which the neutralization product is also highly soluble - calcium acetate...)
Anyway, could be that it's not always the best to follow the best...