kripken/emscripten — pull request #1300 by Manny-MADE (2013-06-16 16:39:08+00:00)
Title: BUGFIX: lists cannot be llvm_va_copy was broken, didn't copy list offset

It seems va_list handling is seriously broken and incompatible.
Check out this testcase, the output at the top of the page is from the native executable https://dl.dropboxusercontent.com/u/20452169/drahtwerk/vabug.html
Here is the corresponding cpp code https://dl.dropboxusercontent.com/u/20452169/drahtwerk/vabug.cpp

The pull request fixes the issue and the tests run identical to native code.