This error has haunted me for several months:
4 [main] head (6660) C:\...\usr\bin\head.exe:r *** fatal error - cygheap base mismatch detected - 0x612C7410/0xAF7410. This problem is probably due to using incompatible versions of the cygwin DLL. Search for cygwin1.dll using the Windows Start->Find/Search facility and delete all but the most recent version. The most recent version *should* reside in x:\cygwin\bin, where 'x' is the drive on which you have installed the cygwin distribution. Rebooting is also suggested if you are unable to find another cygwin DLL.
The tricky part is I am not even using Cygwin. I'm running bash with Git for Windows as published at the official website.
I've tried suggested solution from the error message, googled around quite a bit, I've even dabbled with Windows Security settings (ASLR) - nothing helped and have almost made my peace with the fact that every fifth commandline action will fail loudly.
And yet after recent release I've decided to try one more time. This time I've downloaded the portable build for 64-bit architecture, and it worked! I don't know if it was the fact that I was previously running a 32-bit Git and bash on 64-bit Windows 7 or if Git maintainers have tweaked their build process for 2.23.
If you're experiencing segmentation faults while running bash from Git for Windows package, you should check for architecture mismatch with your OS and/or for newer (2.23+) Git version.