Atoll

[Ike]

I'm having a problem setting water depth to -1 to build a shallow water Atoll.

I set down a section of water, all -3 depth by default. Go to a water hex, hit shift+8. (Spanish keyboard)Brings up "Set terrain height" I type in -1 and enter. The water hex now reads -1, ok. Then when I click a different water hex to set another water hex to -1 the original water hex I set to -1 reverts back to the standard -3 water hex.

What am I doing wrong here?