What version of Go are you using (go version)?

go version go1.7.1 linux/amd64

What operating system and processor architecture are you using (go env)?

amd64, Arch Linux

What did you do?

Mistaken and imported a package from vendor and ran go build

What did you expect to see?

package poc
        imports testpack2
        imports poc/vendor/testpack: use of vendored package not allowed

What did you see instead?

internal error: duplicate loads of poc/vendor/testpack

Extended info

PoC: https://github.com/utrack/golang-poc-17119

It seems that if main imports packages A,B and package B imports vendor/A then the compiler or linker fails with non-descriptive error. See minimal PoC @ repo provided; copy it to $GOPATH/src and try to go build poc.