diff --git a/searx/engines/command.py b/searx/engines/command.py
index b9e672ff..1b73861f 100644
--- a/searx/engines/command.py
+++ b/searx/engines/command.py
@@ -14,8 +14,8 @@ along with searx. If not, see < http://www.gnu.org/licenses/ >.
 '''
 
 
+import re
 from os.path import expanduser, isabs, realpath, commonprefix
-from re import MULTILINE, search as re_search
 from shlex import split as shlex_split
 from subprocess import Popen, PIPE
 from time import time
@@ -59,7 +59,7 @@ def init(engine_settings):
     if 'parse_regex' in engine_settings:
         parse_regex = engine_settings['parse_regex']
         for result_key, regex in parse_regex.items():
-            _compiled_parse_regex[result_key] = re.compile(regex, flags=MULTILINE)
+            _compiled_parse_regex[result_key] = re.compile(regex, flags=re.MULTILINE)
     if 'delimiter' in engine_settings:
         delimiter = engine_settings['delimiter']
 
diff --git a/searx/engines/scanr_structures.py b/searx/engines/scanr_structures.py
index 6dbbf4fd..72fd2b3c 100644
--- a/searx/engines/scanr_structures.py
+++ b/searx/engines/scanr_structures.py
@@ -11,7 +11,7 @@
 """
 
 from json import loads, dumps
-from urllib.parse import html_to_text
+from searx.utils import html_to_text
 
 # engine dependent config
 categories = ['science']
diff --git a/searx/webadapter.py b/searx/webadapter.py
index e2867d99..7c71b726 100644
--- a/searx/webadapter.py
+++ b/searx/webadapter.py
@@ -122,9 +122,6 @@ def parse_specific(raw_text_query: RawTextQuery) -> Tuple[List[EngineRef], List[
 
 
 def parse_category_form(query_categories: List[str], name: str, value: str) -> None:
-    if is_locked('categories'):
-        return preferences.get_value('categories')
-
     if name == 'categories':
         query_categories.extend(categ for categ in map(str.strip, value.split(',')) if categ in categories)
     elif name.startswith('category_'):
@@ -145,7 +142,7 @@ def parse_category_form(query_categories: List[str], name: str, value: str) -> N
 def get_selected_categories(preferences: Preferences, form: Optional[Dict[str, str]]) -> List[str]:
     selected_categories = []
 
-    if form is not None:
+    if not is_locked('categories') and form is not None:
         for name, value in form.items():
             parse_category_form(selected_categories, name, value)
 
@@ -181,15 +178,17 @@ def parse_generic(preferences: Preferences, form: Dict[str, str], disabled_engin
 
     # set categories/engines
     explicit_engine_list = False
-    for pd_name, pd in form.items():
-        if pd_name == 'engines':
-            pd_engines = [EngineRef(engine_name, engines[engine_name].categories[0])
-                          for engine_name in map(str.strip, pd.split(',')) if engine_name in engines]
-            if pd_engines:
-                query_engineref_list.extend(pd_engines)
-                explicit_engine_list = True
-        else:
-            parse_category_form(query_categories, pd_name, pd)
+    if not is_locked('categories'):
+        # parse the form only if the categories are not locked
+        for pd_name, pd in form.items():
+            if pd_name == 'engines':
+                pd_engines = [EngineRef(engine_name, engines[engine_name].categories[0])
+                              for engine_name in map(str.strip, pd.split(',')) if engine_name in engines]
+                if pd_engines:
+                    query_engineref_list.extend(pd_engines)
+                    explicit_engine_list = True
+            else:
+                parse_category_form(query_categories, pd_name, pd)
 
     if explicit_engine_list:
         # explicit list of engines with the "engines" parameter in the form
@@ -234,7 +233,7 @@ def get_search_query_from_webapp(preferences: Preferences, form: Dict[str, str])
     query_timeout = parse_timeout(form, raw_text_query)
     external_bang = raw_text_query.external_bang
 
-    if raw_text_query.enginerefs and raw_text_query.specific:
+    if not is_locked('categories') and raw_text_query.enginerefs and raw_text_query.specific:
         # if engines are calculated from query,
         # set categories by using that informations
         query_engineref_list, query_categories = parse_specific(raw_text_query)