git checkout branch puzzle

I have been using msysgit (curently 1.7.0.2.msysgit.0) for about 18 months and thought that I had managed to understand most things. However, the following sequence has me baffled:

a) on branch 'master', git status shows that the working directory is clean

b) git checkout HEAD^ gives the usual moan about moving to a head which isn't a local branch

c) git checkout master followed by git status gives "changed but not updated" and a list of "modified" files

d) git reset --hard does not change the situation

I suspect the situation arose as a result of 'mv'ing some files without using git mv, but the resulting state above seems unreasonable.

Any explanation of (c)/(d) would be appreciated.

As a result, I have started using git add -A rather than got add . (and wonder why it isn't documented as the default thing to do).

TIA for any light on this.