Mission Planner 1.3.53.0 Verify Height bug

#### Issue details
Using Verify Height and Relative Altitude, Mission Planner plans using Absolute Altitude values.
If Verify Height is unchecked, the plan is created for a fixed Relative Altitude, as expected.
Verify Height + Absolute also behaves as expected. But Verify Height + Relative gives the same plan.

#### Version
1.3.52.0

#### Platform

I have Mission Planner installed on 3 different platforms (2 desktop PCs and a laptop), all running Windows 10 (possibly different builds), with Spanish system language.

This error occurs on the PCs, but not on the laptop.

I am planning missions without connection to the drone. On the two PCs, Mission Planner has never been connected to the drone, nor set up for a particular firmware. The laptop has been used with the drone in the past.

Start by reproducing the Mission Planner planning flow with Verify Height and Relative Altitude enabled, comparing it with Verify Height unchecked and with Absolute Altitude. Check whether the result differs across the reported Windows 10 and Spanish-language configurations. Done means Relative Altitude produces a fixed relative-altitude plan consistently while the other documented behaviors remain unchanged.

Written by the indexing model from the issue text.