I did a pretty deep usage of StackPanels inside ScrollViewers in the BabylonChat project, and didn’t have this issues (I had others 
, don’t worry). But like @mawa notices, I think I mainly inserted rectangles, instead of directly inserting TBs.
That said, I’m not familial with the GUI editor (I did the chat only using code), but having a look at your links, I’m quite surprised :
- On my side I have the indentation on both Playground and GUI editor (it seems that PG adds nothing which is not in the editor, on my side)
- Having a look at the textBlocks in the editor, they all have a hardcoded padding on X, which seems to be the reason of the shift :
(default) 30 pixels of padding :
Manually going back to 0 :
Is it intended ? 
++
Tricotou