Widget pos not respected on first render

Steps:
- Set 'Details Viewer' widget pos to 0 and '2D Viewer' widget pos to 1

Expected:
- Widget tab order is maintained since the first render

Result:
- Only posterior renders maintain the position

https://user-images.githubusercontent.com/19196034/194919259-d9d8079e-6ec9-42a6-89c0-8c928d34f24f.mp4

Start by reproducing the reported setup with Details Viewer at position 0 and 2D Viewer at position 1, then trace the widget initialization and first-render path. Done means the tab order is correct on the initial render as well as on subsequent renders.

Written by the indexing model from the issue text.