Tested again, same results.
R20.059
case 2: <user_prefs>\plugins unchecked, D:\R20plugins checked
-> restart -> no collision
R21.026
case 3: <user_prefs>\plugins checked -> no collision.
I really don't get this as I remember having had collisions when I first tried this.
I have tried following:
Removed all paths from the preferences, restart Cinema 4D. Obviously, plugins are loaded due to the default folder, and no collisions since no other path is defined.
I then add the <user_prefs>\plugin folder again, checkbox enabled. Restart -> no collisions.
Went a step further:
I had the <user_prefs>\plugins folder added, then added the <user_prefs> folder (without the "plugins" subfolder) -> restart -> no collision
Went even crazier:
With above 2 paths available (and enabled), I added D:\R21plugins
-> restart -> collisions !!!
Final case:
removed the D:R21plugins, then copied the plugins in the <user_prefs>
resulting in
<user_prefs>\plugins
<user_prefs>\plugins - Copy
Added both paths to the preferences, both enabled -> restart -> collisions
Removed the copy path from the preferences keeping only <user_prefs>\plugins
-> restart -> no collision
Cannot explain the behavior.
I think I will stop the whole topic here, it seems to make no sense at all.