The error on the facade

It’s a professional perversion of mine to discover typographical and generally language errors. In my mother tongue this is easy, as I’m very familiar with it, but recently it happens to me with english and other languages I happen to speak.
Some weeks ago, I took a short trip to Erfurt, the beautiful capital of Thuringia in Germany. The city with its many imposing medieval churches and monasteries, its large historical centre, many renaissance and baroque buildings, is a very attractive tourist destination.
There is a beautiful street called the Anger, a Cathedral with something of a twin church or annex, many theatres, and a river running inside the lively city with its many students and other inhabitants.
There is also a square called Fischmarkt, where you just can’t stop admiring the buildings. They are so impressive.
It was there I spotted an error on a façade. A medieval building called “The house of the red ox” (thanks to a frieze depicting such an animal) served as one of the first cinemas in the beginning of the 20th century and is today a modern art gallery. Apart from the ox, the façade is decorated with the 9 Muses and the name of one of them “Polymnia” is written “Polynmia”. Was it a mistake of the original artist back in 1392 when the house was first constructed or maybe in 1562 was it thus spelt by its new owner who made a few changes in its style?
I asked the very polite young lady who must have been the curator of the interesting temporary exhibition (photos from war zones) hosted inside,  but she didn’t know. It seems that no one else had spotted the error on the façade. It took a Greek to recognize an error regarding a greek name, I suppose. In the photo I took, you can’t really see what I’m talking about, but the Muse Polymnia (Polyhymnia) is the third one from left.
Anyway, Erfurt is worth a visit or more and if you happen to pass by the nearby Molsdorf Palace, it’s worth stopping there as well.