Why is mangling different for separate compilation?

[Walter Bright via Digitalmars-d]

On 2/26/2016 4:45 AM, Atila Neves wrote:
> '_D3bar16__unittestL2_531FZv'
> '_D3bar14__unittestL2_1FZv'

It uses a sequence number to generate different ids for the unit tests. In the 
former, it's the 531st unit test, the latter, the first.