Altitude doesn't change (much) at the point where an orbit raising maneuver is performed. It increases the altitude of the rest of the orbit, with the greatest change ~180 degrees later.

If you'll excuse some poor ASCII art:

                                       _______
                  ______              /       \
                 /      \            /         \
    burn here -> *    O |    result: |    O    |
  in elliptical  \______/            \         /
    orbit                             \_______/