diff --git a/cpex/framework/loader/config.py b/cpex/framework/loader/config.py
index a7b1eb70..144b9e7f 100644
--- a/cpex/framework/loader/config.py
+++ b/cpex/framework/loader/config.py
@@ -70,7 +70,15 @@ def load_config(config: str, use_jinja: bool = True) -> Config:
             with open(os.path.normpath(config), "r", encoding="utf-8") as file:
                 template = file.read()
                 if use_jinja:
-                    jinja_env = SandboxedEnvironment(loader=jinja2.BaseLoader(), autoescape=True)
+                    # Use DebugUndefined so that ONLY `env.*` references (the values passed to
+                    # render()) are substituted; any other ``{{ ... }}`` in the config — e.g. a
+                    # plugin's default_template that it renders itself at runtime — is left
+                    # verbatim as ``{{ name }}`` instead of being silently blanked to "".
+                    # Without this, the default Undefined renders every non-env placeholder to an
+                    # empty string at load time, so a plugin that stores a runtime template in its
+                    # config (WebhookNotification's default_template) ends up with an all-empty,
+                    # invalid body. See issue #81.
+                    jinja_env = SandboxedEnvironment(loader=jinja2.BaseLoader(), autoescape=True, undefined=jinja2.DebugUndefined)
                     rendered_template = jinja_env.from_string(template).render(env=os.environ)
                 else:
                     rendered_template = template
diff --git a/tests/unit/cpex/framework/loader/test_config_loader.py b/tests/unit/cpex/framework/loader/test_config_loader.py
new file mode 100644
index 00000000..32d9be51
--- /dev/null
+++ b/tests/unit/cpex/framework/loader/test_config_loader.py
@@ -0,0 +1,74 @@
+# -*- coding: utf-8 -*-
+"""Location: ./tests/unit/cpex/framework/loader/test_config_loader.py
+Copyright 2025
+SPDX-License-Identifier: Apache-2.0
+Authors: Tao Peng
+
+Regression tests for ConfigLoader's jinja rendering (issue #81).
+
+The jinja pass in ``ConfigLoader.load_config`` must substitute ``env.*`` references
+while leaving any OTHER ``{{ ... }}`` placeholder verbatim — so a plugin that stores
+a runtime template in its config (e.g. WebhookNotification's ``default_template``) is
+not silently blanked at load time.
+"""
+
+# Standard
+import os
+import tempfile
+
+# First-Party
+from cpex.framework.loader.config import ConfigLoader
+
+# A config whose plugin carries BOTH an env reference (must be substituted) and a
+# non-env runtime template placeholder (must be preserved, not blanked).
+_CONFIG = """plugins:
+  - name: "TemplatePlugin"
+    kind: "plugins.example.TemplatePlugin"
+    hooks: ["prompt_pre_fetch"]
+    config:
+      endpoint: "{{ env.CPEX_TEST_ENDPOINT }}"
+      default_template: '{ "event": "{{event}}", "timestamp": "{{timestamp}}", "violation": "{{violation}}" }'
+"""
+
+
+def _load(config_text: str, use_jinja: bool = True):
+    """Write ``config_text`` to a temp file and load it through ConfigLoader."""
+    with tempfile.NamedTemporaryFile(mode="w", suffix=".yaml", delete=False, encoding="utf-8") as handle:
+        handle.write(config_text)
+        temp_path = handle.name
+    try:
+        return ConfigLoader.load_config(temp_path, use_jinja=use_jinja)
+    finally:
+        os.unlink(temp_path)
+
+
+def test_jinja_substitutes_env_reference(monkeypatch):
+    """An ``{{ env.X }}`` reference is substituted with the environment value."""
+    monkeypatch.setenv("CPEX_TEST_ENDPOINT", "https://hooks.example.com/abc")
+    config = _load(_CONFIG)
+    assert config.plugins[0].config["endpoint"] == "https://hooks.example.com/abc"
+
+
+def test_jinja_preserves_non_env_placeholder(monkeypatch):
+    """Issue #81: a non-env ``{{ ... }}`` (a plugin's runtime template) is NOT blanked.
+
+    Before the fix, the default Undefined rendered every non-env placeholder to an
+    empty string at load time, leaving ``default_template`` as
+    ``{ "event": "", "timestamp": "", "violation": "" }``.
+    """
+    monkeypatch.setenv("CPEX_TEST_ENDPOINT", "https://hooks.example.com/abc")
+    config = _load(_CONFIG)
+    template = config.plugins[0].config["default_template"]
+    # The runtime placeholders survive load (whitespace is normalized to `{{ name }}`).
+    assert "{{ event }}" in template
+    assert "{{ timestamp }}" in template
+    assert "{{ violation }}" in template
+    # And it was NOT blanked.
+    assert '"event": ""' not in template
+
+
+def test_jinja_disabled_leaves_template_untouched():
+    """With ``use_jinja=False`` nothing is rendered — env refs stay literal too."""
+    config = _load(_CONFIG, use_jinja=False)
+    assert config.plugins[0].config["endpoint"] == "{{ env.CPEX_TEST_ENDPOINT }}"
+    assert "{{event}}" in config.plugins[0].config["default_template"]