Your input#employee is not going to be re-rendered by changing Session.get('employee-number') because it does not depend on that or any other Session value. My guess is that you were previously relying on something higher up the DOM triggering a re-rendering of the entire template when Session.get('employee-number') changed.
That is a major change in Meteor 0.8+ - a change in a reactive data source will not automatically trigger re-rendering of an entire template, but only those specific elements that depend on the data source. So input#employee is not being re-rendered.
I would read here for more information on this change.
Also, as a side note, Iron Router's 'before' hook is being deprecated in favor of 'onBeforeAction'. This is likely not the source of your question because 'before' will be supported through Meteor 1.0 (see here). Just wanted to point it out for future-proofing.