[ !!! EDIT : Well, actually, I tried that path again and strangely nothing happen. So it was reproductible on purpose during the previous session but not on the next one. But anayway, at least, I can assume it occured at 3 differents sessions from 2 differents servers in single mode, so I'll looking for it each in the next sessions and keep the log !!! ]
How to bypass the restriction :
# Choose an unrotatable block (i. e. Power Capacitor).
# Memorize its default orientation.
# Place it.
# Take a rotable block (i. e. Hull Wedge).
# Change its orientation.
# Come back to the unrotatable block.
# Place it.
# Bypass complete.