I do not know what library contains bad sprintf function.
Maybe you can figure it out using (foreign-address #<foreign-function>) and see if you can relate that to the addresses of the .dll loaded into the current process?
I have found it! This is ntdll.dll (in this library still more many other functions). F&%k!
It is caused from ole32.dll.
win32 *.dll hell...
Use CFFI with Windows without cpecification of library is problematic :(
Thanks!