Show changes as unified diff fails (using Cygwin git)

I'm using TortoiseGit with Cygwin git (Cygwin hack enabled in advanced TortoiseGit settings). For the most part, everything works correctly. The only problem: in TortoiseGit log for any repository, right-click any commit, pick "show changes as unified diff", there's an error dialog:

Could not get unified diff.
   1 [main] git 2292 child_copy: cygheap read copy failed,
0x180302408..0x18030F230, done 0, windows pid 2292, Win32 error 6
411 [main] git 2292 C:\cygwin\bin\git.exe: *** fatal error - ccalloc
would have returned NULL

Actually I've had this several months ago, just never got around to posting this to the list.

TortoiseGit 2.3.0.0 Cygwin 64-bit 2.876 Cygwin git 2.8.3-1 Windows 7 x64