Reproduction steps:
1. Open or create any Unity project
2. Create TextMeshPro Text GameObject
3. Rotate x-axis by at least 180 degrees
4. Select the vertical white square gizmo and try slightly increasing the margins

Expected result: Margins get increased by the amount mouse has moved
Actual result: Margins get increased by millions and become NaNs soon after

Reproducible with: 2018.4.26f1, 2019.4.5f1, 2020.1.0f1, 2020.2.0a19
Reproducible with the package versions: 1.2.0, 1.5.0, 2.0.1, 2.1.1, 3.0.0-preview.1, 3.0.0

Notes:
1. The issue reproduces with both 2D and 3D TMP components
2. The issue most visibly reproduces when the rotation is between 90 and 180 degrees. Smaller rotations lead to the handle being non-intuitive, but scaling is not visibly affected.