Strange b2 headers problem

From: Edward Diener (eldiener_at_[hidden])
Date: 2021-08-24 00:38:02

I switched my main boost repository from the 'develop' branch to an 
earlier tagged boost release to try something out in that earlier 
release. Everything went fine with switching the main repository and all 
submodules. I wiped out all the header links  from the boost 
subdirectory and I tried b2 headers, only to get:

error: Cannot create link boost\property_map\parallel\basic_reduce.hpp 
to 
libs\property_map_parallel\include\boost\property_map\parallel\basic_reduce.hpp.
error: Link previously defined to another file, 
libs\property_map\include\boost\property_map\parallel\basic_reduce.hpp.

This makes no sense since there is a completely empty boost subdirectory 
under my main boost repository directory. How do I fix this problem ?