4003 – The result changes only with the order of source files.

from http://dusers.dip.jp/modules/forum/index.php?post_id=220
The bug occurred with changing the order of import, or order of files as compiler options.
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main.d
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import std.stdio;
void main(){}
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test.d
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import std.typecons;
Tuple!(string) t;
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Case of success:
dmd -unittest test.d main.d
Case of failure:
dmd -unittest main.d test.d
std\typecons.d(424): Error: static assert (is(Tuple!(string,float) == Tuple!(string,float))) is false
std\typecons.d(413): instantiated from here: Tuple!(string,float)
...

*** Issue 4294 has been marked as a duplicate of this issue. ***

I'm raising the importance of this. Every time your program uses two Phobos modules that both import std.typecons, you risk running into this bug.
See bug 4294 for a marginally more narrow test case.

http://www.dsource.org/projects/dmd/changeset/527 

*** Issue 4299 has been marked as a duplicate of this issue. ***

Commit pushed to master at https://github.com/D-Programming-Language/dmd
https://github.com/D-Programming-Language/dmd/commit/79f0913b6f84ef60068079a0f18673f114cf1ef5
Remove phobos dependency from issue 4003 test case