incomprehensible bug with import side effects

[timotheecour]

I've filed the following bug: see Issue 8854 
(http://d.puremagic.com/issues/show_bug.cgi?id=8854)
I'm curious as to what could cause such a bug, which disappears 
when doing any of the following seemingly innocuous changes, such 
as change a file name, change an import path, removing an 
(unused) import std.stdio statement, etc.