Use space (' ') instead of '?' as a pattern terminator.
diff --git a/git-flow-hotfix b/git-flow-hotfix
index e7ff5e2..0b4ab25 100644
--- a/git-flow-hotfix
+++ b/git-flow-hotfix
@@ -38,7 +38,7 @@
 		exit 0
 	fi
 	current_branch=$(git branch | grep '^\* ' | grep -v 'no branch' | sed 's/^* //g')
-	short_names=$(echo "$hotfix_branches" | sed "s?^$PREFIX??g")
+	short_names=$(echo "$hotfix_branches" | sed "s ^$PREFIX  g")
 
 	# determine column width first
 	typeset -i width=0