Namespace weirdness with AS3

For my recent pet project (Displaying an Excel Sheet in Flash) i ran into a strange behaviour along with namespace usage. The Class responsible for loading and displaying the XML had a namespace variable initialised and set later on once the XML loaded and the namespace therein was read. But now the main Timeline threw an error with every function telling me the namespace variable was not defined- WHAT THE **?

Soon as I declared the variable with a dummy value on the Main Timeline, my FLA compiled succesfully with no errors. Someone please explain that to me...