When Vancouver Public Schools staff and students left for the holiday break last month, Superintendent Steve Webb sent them off with some good news. The district and its support staff union had reached a tentative agreement, ending months of contentious negotiations. Now, nearly a month later, the two sides are at odds over a key component of that agreement: whether it exists at all. Leadership and members of the Vancouver Association of Educational Support Professionals said Tuesday that the district has backed out of the tentative agreement.