diff --git a/manimlib/mobject/svg/string_mobject.py b/manimlib/mobject/svg/string_mobject.py
index c393019a..08a3c73d 100644
--- a/manimlib/mobject/svg/string_mobject.py
+++ b/manimlib/mobject/svg/string_mobject.py
@@ -36,7 +36,7 @@ class StringMobject(SVGMobject, ABC):
     or a 2-tuple containing integers or None, or a collection of the above.
     Note, substrings specified cannot *partly* overlap with each other.
 
-    Each instance of `StringMobject` generates 2 svg files.
+    Each instance of `StringMobject` may generate 2 svg files.
     The additional one is generated with some color commands inserted,
     so that each submobject of the original `SVGMobject` will be labelled
     by the color of its paired submobject from the additional `SVGMobject`.
@@ -546,15 +546,11 @@ class StringMobject(SVGMobject, ABC):
         ])
 
     def select_parts(self, selector: Selector) -> VGroup:
-        indices_list = self.get_submob_indices_lists_by_selector(selector)
-        if indices_list:
-            return self.build_parts_from_indices_lists(indices_list)
-        elif isinstance(selector, str):
-            # Otherwise, try finding substrings which weren't specifically isolated
-            log.warning("Accessing unisolated substring, results may not be as expected")
+        specified_substrings = self.get_specified_substrings()
+        if isinstance(selector, str) and selector not in specified_substrings:
             return self.select_unisolated_substring(selector)
-        else:
-            return VGroup()
+        indices_list = self.get_submob_indices_lists_by_selector(selector)
+        return self.build_parts_from_indices_lists(indices_list)
 
     def __getitem__(self, value: int | slice | Selector) -> VMobject:
         if isinstance(value, (int, slice)):