git grep searches for a pattern in the complete content of a commit (not just the changes it introduced).
If somePattern is present in any other file (including a file not changed in the stash), you will see an output.
If you want to spot files where the changes contain the pattern, instead of git grep, try one of :
git show -S somePattern stash@{1} # or : git show -G somePattern stash@{1} In your case : it looks like the pattern you are looking for is not inpart of the changes of stash@{1}.
If you want to inspect the content of all your stash entries, use one of the -S or -G options on git reflog stash :
# * you also need the '-m' option when inspecting the stash, because all # stash entries are actually merge commits # * '-p' will print the patch of files matching the pattern, and will # allow you to see if those are the changes you are looking for git reflog --oneline -m -S somePattern -p stash