Wisconsin State Journal Editorial:

The district proposed to add two more HMO options for teachers. If a teacher chose any of the three HMO options, the district would pay the full premium. But if a teacher chose the high-cost WPS option, the district would pay only up to the cost of the highest-priced HMO plan. The teacher would be responsible for the remainder.
The change would have saved the district enough money to permit salaries to increase 2.8 percent, rather than 1 percent.
Madison Teachers Inc., however, resisted. Although bargaining units for food service workers, custodians and other district employees had accepted similar changes to their health insurance plans, the teachers union preferred to sacrifice higher pay to maintain the WPS health insurance option.
The School Board’s mistake was to cave in to the union’s position. While the cost to taxpayers was the same whether money was devoted to health insurance or salaries, it was in the district’s long-term interest to control health insurance costs and shift more money to salaries.

Audio / Video and links of the Madison School Board’s discussion and vote on this matter.
Lawrie Kobza’s statement.
MTI’s John Matthews offers a different perspective:

he union is obligated to represent its members interests. The union surveyed its members prior to entering bargaining and the members spoke loudly and clearly: Retain our health insurance options.
MTI members value Wisconsin Physicians Service because it enables freedom of choice in medical providers. And MTI members value the services of Group Health Cooperative. However, both GHC and WPS coverage would be in jeopardy under the district’s proposal.
GHC has the option of increasing its premium by 2 percent for each additional HMO offered by the district. Adding other HMOs would undercut the financial base of employees necessary to maintain the foundation of the WPS option.
Insurance is supposed to assure economic stability. Revenue controls undercut this basic principal of employment benefits, as it causes even the best intentioned individuals to think about reducing the quality of insurance to provide wages. MTI members have not been willing to take that risk.