Hi,
I've encountered the same bug and experimented a little
I've tried some workarounds found on internet from probably earlier version without success (rebuild foundations, build one fundation under the read fundation)
I'm on stable (not experimental) version and used large areas of 8x1 fundations in my tests
The rotation of the building and the building itself have an influence on the forbidden zone wich seems to be a line
For manufacturer, being aligned on the foundation grid with manufacturer output towards you, If you move left / right, you will see equally spaced forbidden node (output aligned with foundations junctions or with the center of the foundation), if you stop at one forbidden node and move forward / backward all nodes on this line are forbidden
For constructor it's the opposite : move forward backward till a forbidden node then all the left / right line is invalid (but no apparent alignment rulez the forbidden node as the manufacturer)
Assemblers doesn't seem to be affected
This bug is recent from the last patch as all my manufacturer output are aligned with the center of a foundation, if I remove one, I can't rebuild it at the same place
After writing all this above, I realized I didn't test other foundations and thought I should before submiting this :
Only 8x1 foundations have this bug so a dirty (and painful on wide builds) workaround that worked for me should be to replace 8x1 by any other, place the manufacturer then replace foundations with 8x1
Hope this will help to fix 