This is more of an annoyance than a real show-stopper bug, but I'd like to know if anybody else experiences the same issue:
When I use a healing spell of any rank for the first time after logging in, the estimated amount of healing is not shown. Subsequent uses of the same spell will be displayed correctly with the amount of heal/overheal. However, when I pick another healing spell (e.g. Lesser Healing Wave), the same issue occurs - no estimated heal / overheal for the first heal, and then the display works correctly for any subsequent heals.