git commit logs CREATE and COPY multiple times with curly brackets - Why?

git commit logs CREATE and COPY multiple times with curly brackets - Why?

Recently I analysed the commit log of my local repo and noticed the
following and I would like to know what is happening here. Can anybody
give an answer or a pointer to a web site explaining this?
Let's say I have the following file structure:
/path/a.txt
/path/b.txt
/path/c.txt
/path/d.txt
When I commit it, I saw the following in the log:
create mode 100644 path/a.txt
create mode 100644 path/b.txt
copy path/{a.txt => b.txt} (100%)
create mode 100644 path/c.txt
copy path/{a.txt => c.txt} (100%)
create mode 100644 path/d.txt
copy path/{a.txt => d.txt} (100%)
all files are completely different content-wise. So what do those curly
brackets {=>} mean?
Git version: 1.7.0.4 (don't ask me why I am not using the latest version,
it's a client's server where I can not just install the latest version.)