When I have seen mushrooms propagate they actually will move and leave a little bit of themselves behind where their foot was attached - then this turns into a new shroom. You can almost see a trail of babies as it moved over the rock work over a period of time.
I have also seen polyps split like that as a last ditch effort to save itself. A survival instinct I suppose, where they are not happy for whatever reason, stress then split. Given you have two doing it at the same time, I would suggest the splitting is a reaction to something rather than a happy shroom leaving babies. I would verify your parameters, and work backward on whatever might have changed recently.
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- Paul made me do it
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