CTRL+Z switches Height-Mode

#### Issue details
When planning a mission and pressing CTRL+Z to undo a change, the height-mode (Relative, Terrain, Absolute) switches back to "Relative", no matter what has been selected before.

#### Version
I am using MP 1.3.74 build 1.3.7563.27684

#### Platform
We are using MP to plan routes for Copters, I do not know if this affects other platforms as well.

[ ] All
[ ] AntennaTracker
[x] Copter
[ ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
This should not matter as this issue affects the planning feature

#### Hardware type
This should not matter as this issue affects the planning feature
MP runs on Windows 10 with latest updates.

#### Logs
I do not know about any logs that would help here, but if I can provide you with any logs, just let me know.

No source file or test is identified in the issue. Reproduce this in Mission Planner's mission-planning view by selecting a height mode and pressing CTRL+Z; investigate the undo path and height-mode state. Done means undoing a change preserves the previously selected Relative, Terrain, or Absolute mode.

Written by the indexing model from the issue text.