diff --git a/lib/markdown2.py b/lib/markdown2.py
index 330ddea8..194a23d7 100755
--- a/lib/markdown2.py
+++ b/lib/markdown2.py
@@ -2584,7 +2584,7 @@ class GFMItalicAndBoldProcessor(Extra):
     def run(self, text: str):
         nesting = True
         orig_text = ""
-        while nesting and orig_text != _hash_text(text):
+        while nesting or orig_text != _hash_text(text):
             orig_text = _hash_text(text)
             nesting = False
 
@@ -2838,6 +2838,7 @@ def should_process_imbalanced_delimiter_runs(
         open_syntax = open.group(1)[open_offset:]
 
         syntax = close.group(1)
+        em_type = syntax[0]
         left, right = self.delimiter_left_or_right(close)
 
         if len(open_syntax) < len(syntax) and len(syntax) >= 3:
@@ -2845,7 +2846,8 @@ def should_process_imbalanced_delimiter_runs(
             # open em spans
             return True
 
-        if next_delim_run is None:
+        # if no delimiter run after OR the next run is of a different syntax
+        if next_delim_run is None or next_delim_run[0].group(1)[0] != em_type:
             return True
 
         if len(open_syntax) < len(syntax) and (
@@ -3450,12 +3452,10 @@ def process_span(self, open: re.Match[str], close: re.Match[str], offset: int, m
         open_syntax = open.group(1)[offset:]
         close_syntax = close.group(1)
 
-        if len(open_syntax) > 2 or open_syntax != close_syntax:
-            return [text], None
-
         if '_' in open_syntax:
+            min_syntax = min(open_syntax, close_syntax)
             # if using _this_ syntax, hash it to avoid processing, but don't hash the contents incase of nested syntax
-            text = text.replace(open_syntax, _hash_text(self.name + open_syntax))
+            text = text.replace(min_syntax, _hash_text(self.name + min_syntax))
             return [text], None
         elif '_' in text:
             # if the text within the bold/em markers contains '_' then hash those chars to protect them from em_re
diff --git a/test/tm-cases/code_friendly_issue671.html b/test/tm-cases/code_friendly_issue671.html
new file mode 100644
index 00000000..1f41b82d
--- /dev/null
+++ b/test/tm-cases/code_friendly_issue671.html
@@ -0,0 +1,3 @@
+<p>__A___B_C_D_E_F_G</p>
+
+<p><strong>A_B</strong> <a href="https://example.com/">C_D_E</a></p>
diff --git a/test/tm-cases/code_friendly_issue671.opts b/test/tm-cases/code_friendly_issue671.opts
new file mode 100644
index 00000000..8eb3b9ef
--- /dev/null
+++ b/test/tm-cases/code_friendly_issue671.opts
@@ -0,0 +1 @@
+{'extras': ['code-friendly']}
\ No newline at end of file
diff --git a/test/tm-cases/code_friendly_issue671.text b/test/tm-cases/code_friendly_issue671.text
new file mode 100644
index 00000000..f3e9bb83
--- /dev/null
+++ b/test/tm-cases/code_friendly_issue671.text
@@ -0,0 +1,3 @@
+__A___B_C_D_E_F_G
+
+**A_B** [C_D_E](https://example.com/)
\ No newline at end of file
diff --git a/test/tm-cases/gfm_emphasis_issue671.html b/test/tm-cases/gfm_emphasis_issue671.html
new file mode 100644
index 00000000..16f51368
--- /dev/null
+++ b/test/tm-cases/gfm_emphasis_issue671.html
@@ -0,0 +1,7 @@
+<p><em>A-></em><strong>B</strong></p>
+
+<p><strong>A-></strong><strong>B</strong></p>
+
+<p>*<em>A</em> B_<em>C</em></p>
+
+<p>*<em>A</em> B C_D. X Y Z *</p>
diff --git a/test/tm-cases/gfm_emphasis_issue671.text b/test/tm-cases/gfm_emphasis_issue671.text
new file mode 100644
index 00000000..1a045d70
--- /dev/null
+++ b/test/tm-cases/gfm_emphasis_issue671.text
@@ -0,0 +1,7 @@
+*A->***B**
+
+**A->****B**
+
+**A* B_*C*
+
+**A* B C_D. X Y Z *