I had heard this also. However, when I went to the Kreisbüro in Zürich and told them I would only be there a month then move to Aargau the lady even suggested I not register in Zürich at all and try to register with Aargau straight away as it would save me time & money. I've been back to the Kreisbüro a couple of times and talked to several different people. None of them gave any indication that there would be problems. In fact, they were all very helpful and affable people.