That doesn't sound right, but maybe there is something about the Spanish law I don't know. You can transition to other countries tax residency in Germany if you de-register(most countries don't have the concept of de-registering) and enter the other ones without making use of double taxation laws. You do have to notify your local tax authority of leaving though otherwise they'll happily continue treating you like a resident. Usually the overlap is something like a year. Most countries actually have insight into each others tax records nowadays.