diff --git a/nameparser/config/__init__.py b/nameparser/config/__init__.py
index ce9da44..624ef6b 100644
--- a/nameparser/config/__init__.py
+++ b/nameparser/config/__init__.py
@@ -179,7 +179,6 @@ class Constants:
     capitalization_exceptions: TupleManager[str]
     regexes: RegexTupleManager
 
-    _pst: Set[str] | None
 
     string_format = "{title} {first} {middle} {last} {suffix} ({nickname})"
     """
@@ -262,13 +261,10 @@ def __init__(self,
         self.conjunctions = SetManager(conjunctions)
         self.capitalization_exceptions = TupleManager(capitalization_exceptions)
         self.regexes = RegexTupleManager(regexes)
-        self._pst = None
 
     @property
     def suffixes_prefixes_titles(self) -> Set[str]:
-        if not self._pst:
-            self._pst = self.prefixes | self.suffix_acronyms | self.suffix_not_acronyms | self.titles
-        return self._pst
+        return self.prefixes | self.suffix_acronyms | self.suffix_not_acronyms | self.titles
 
     def __repr__(self) -> str:
         return "<Constants() instance>"
diff --git a/tests/test_constants.py b/tests/test_constants.py
index 9f619c3..ca13dc6 100644
--- a/tests/test_constants.py
+++ b/tests/test_constants.py
@@ -104,3 +104,35 @@ def test_add_constant_with_explicit_encoding(self) -> None:
         c = Constants()
         c.titles.add_with_encoding(b'b\351ck', encoding='latin_1')
         self.assertIn('béck', c.titles)
+
+    def test_suffixes_prefixes_titles_reflects_add_title(self) -> None:
+        """suffixes_prefixes_titles must include titles added after construction."""
+        c = Constants()
+        c.titles.add('emerita')
+        self.assertIn('emerita', c.suffixes_prefixes_titles)
+
+    def test_suffixes_prefixes_titles_reflects_add_prefix(self) -> None:
+        """suffixes_prefixes_titles must include prefixes added after construction."""
+        c = Constants()
+        c.prefixes.add('xpfx')
+        self.assertIn('xpfx', c.suffixes_prefixes_titles)
+
+    def test_suffixes_prefixes_titles_reflects_remove_title(self) -> None:
+        """suffixes_prefixes_titles must not include a word that was only in titles and is then removed."""
+        c = Constants()
+        c.titles.add('emerita')
+        self.assertIn('emerita', c.suffixes_prefixes_titles)
+        c.titles.remove('emerita')
+        self.assertFalse('emerita' in c.suffixes_prefixes_titles)
+
+    def test_is_rootname_consistent_with_is_title(self) -> None:
+        """is_rootname must return False for words recognised by is_title."""
+        hn = HumanName("", constants=None)
+        hn.C.titles.add('emerita')
+        self.assertFalse(hn.is_rootname('emerita'))
+
+    def test_is_rootname_consistent_with_is_prefix(self) -> None:
+        """is_rootname must return False for words recognised by is_prefix."""
+        hn = HumanName("", constants=None)
+        hn.C.prefixes.add('xpfx')
+        self.assertFalse(hn.is_rootname('xpfx'))