I enabled appveyor for Boost.DateTime pull requests and they are failing miserably when <cxxstd> is specified more than once. I don't remember this occurring in the past. This happens on Visual Studio, cygwin, mingw builds. Is this new Boost.Build behavior? https://ci.appveyor.com/project/jeking3/date-time-1evbf/build/1.0.3-develop error: Name clash for 'libboost_atomic-vc140-mt-x32-1_67.lib' error: error: Tried to build the target twice, with property sets having error: these incompatible properties: error: error: - <cxxstd>14 error: - <cxxstd>17 error: error: Please make sure to have consistent requirements for these error: properties everywhere in your project, especially for install error: targets. Command exited with code 1