Can we just agree that this is ridiculous and that whomever made the Polish language made it unnecessarily complicated and hard? Bad enough that you have most of your words that change endings all the time depending on your sentence structure but to go and use the same endings as plural in another context is unbelievably bonkers.
I say this with love but Polish is insane!
There are indeed numerous cases of morphological syncretism among the world's languages.
The Sanskrit word for 'bride', for example, seems to have identical forms for the nominative singular and the accusative plural: