diff --git a/docs/grammar.md b/docs/grammar.md
index 69a6704..87912a5 100644
--- a/docs/grammar.md
+++ b/docs/grammar.md
@@ -43,7 +43,7 @@ Literals can be one of:
 * `/regular expression+/`
 * `"case-insensitive string"i`
 * `/re with flags/imulx`
-* Literal range: `"a".."z"`, `"1..9"`, etc.
+* Literal range: `"a".."z"`, `"1".."9"`, etc.
 
 #### Notes for when using a lexer:
 
@@ -145,4 +145,4 @@ If the module path is relative, such as `.path.to.file`, Lark will attempt to lo
 
 ### %declare
 
-Declare a terminal without defining it. Useful for plugins.
\ No newline at end of file
+Declare a terminal without defining it. Useful for plugins.
diff --git a/docs/how_to_use.md b/docs/how_to_use.md
index 95041e4..5113d27 100644
--- a/docs/how_to_use.md
+++ b/docs/how_to_use.md
@@ -52,3 +52,19 @@ class MyTransformer(Transformer):
 new_tree = MyTransformer().transform(tree)
 ```
 
+## LALR usage
+
+By default Lark silently resolves Shift/Reduce conflicts as Shift. To enable warnings pass `debug=True`. To get the messages printed you have to configure `logging` framework beforehand. For example:
+
+```python
+from lark import Lark
+import logging
+logging.basicConfig(level=logging.DEBUG)
+
+collision_grammar = '''
+start: as as
+as: a*
+a: 'a'
+'''
+p = Lark(collision_grammar, parser='lalr', debug=True)
+```
diff --git a/lark/load_grammar.py b/lark/load_grammar.py
index 76c9b10..62bdfc5 100644
--- a/lark/load_grammar.py
+++ b/lark/load_grammar.py
@@ -526,8 +526,12 @@ def import_grammar(grammar_path, base_paths=[]):
     return _imported_grammars[grammar_path]
 
 def import_from_grammar_into_namespace(grammar, namespace, aliases):
+    """Returns all rules and terminals of grammar, prepended
+    with a 'namespace' prefix, except for those which are aliased.
+    """
+
     imported_terms = dict(grammar.term_defs)
-    imported_rules = {n:(n,t,o) for n,t,o in grammar.rule_defs}
+    imported_rules = {n:(n,deepcopy(t),o) for n,t,o in grammar.rule_defs}
 
     term_defs = []
     rule_defs = []
@@ -535,7 +539,10 @@ def import_from_grammar_into_namespace(grammar, namespace, aliases):
     def rule_dependencies(symbol):
         if symbol.type != 'RULE':
             return []
-        _, tree, _ = imported_rules[symbol]
+        try:
+            _, tree, _ = imported_rules[symbol]
+        except KeyError:
+            raise GrammarError("Missing symbol '%s' in grammar %s" % (symbol, namespace))
         return tree.scan_values(lambda x: x.type in ('RULE', 'TERMINAL'))
 
     def get_namespace_name(name):