diff --git a/autoload/youcompleteme.vim b/autoload/youcompleteme.vim
index 673cbfa9..68acc3ea 100644
--- a/autoload/youcompleteme.vim
+++ b/autoload/youcompleteme.vim
@@ -420,6 +420,8 @@ endfunction
 
 
 function! s:OnFileTypeSet()
+  exec s:python_command "ycm_state.SetCurrentBuffer()"
+
   if !s:AllowedToCompleteInCurrentBuffer()
     return
   endif
diff --git a/python/ycm/diagnostic_interface.py b/python/ycm/diagnostic_interface.py
index 4593428c..f3621c10 100644
--- a/python/ycm/diagnostic_interface.py
+++ b/python/ycm/diagnostic_interface.py
@@ -26,7 +26,6 @@ from future.utils import itervalues, iteritems
 from collections import defaultdict, namedtuple
 from ycm import vimsupport
 from ycm.diagnostic_filter import DiagnosticFilter, CompileLevel
-import vim
 
 
 class DiagnosticInterface( object ):
@@ -120,13 +119,12 @@ class DiagnosticInterface( object ):
 
 
   def _UpdateSquiggles( self ):
-    if self._bufnr != vim.current.buffer.number:
-      return
 
     vimsupport.ClearYcmSyntaxMatches()
 
     for diags in itervalues( self._line_to_diags ):
-      for diag in diags:
+      # Insert squiggles in reverse order so that errors overlap warnings.
+      for diag in reversed( diags ):
         location_extent = diag[ 'location_extent' ]
         is_error = _DiagnosticIsError( diag )
 
@@ -202,7 +200,7 @@ class DiagnosticInterface( object ):
 
     for diags in itervalues( self._line_to_diags ):
       # We also want errors to be listed before warnings so that errors aren't
-      # hidden by the warnings; Vim won't place a sign oven an existing one.
+      # hidden by the warnings; Vim won't place a sign over an existing one.
       diags.sort( key = lambda diag: ( diag[ 'kind' ],
                                        diag[ 'location' ][ 'column_num' ] ) )
 
diff --git a/python/ycm/tests/test_utils.py b/python/ycm/tests/test_utils.py
index f6f8cf97..dce230f5 100644
--- a/python/ycm/tests/test_utils.py
+++ b/python/ycm/tests/test_utils.py
@@ -139,6 +139,8 @@ def _MockVimOptionsEval( value ):
 
 def _MockVimMatchEval( value ):
   if value == 'getmatches()':
+    # Returning a copy, because ClearYcmSyntaxMatches() gets the result of
+    # getmatches(), iterates over it and removes elements from VIM_MATCHES.
     return list( VIM_MATCHES )
 
   match = MATCHADD_REGEX.search( value )
diff --git a/python/ycm/tests/youcompleteme_test.py b/python/ycm/tests/youcompleteme_test.py
index e71e4422..5538f1ba 100644
--- a/python/ycm/tests/youcompleteme_test.py
+++ b/python/ycm/tests/youcompleteme_test.py
@@ -524,9 +524,9 @@ def YouCompleteMe_UpdateDiagnosticInterface_PrioritizeErrorsOverWarnings_test(
     assert_that(
       test_utils.VIM_MATCHES,
       contains(
-        VimMatch( 'YcmErrorSection', '\%3l\%8c' ),
         VimMatch( 'YcmWarningSection', '\%3l\%5c\_.\{-}\%3l\%7c' ),
-        VimMatch( 'YcmWarningSection', '\%3l\%3c\_.\{-}\%3l\%9c' )
+        VimMatch( 'YcmWarningSection', '\%3l\%3c\_.\{-}\%3l\%9c' ),
+        VimMatch( 'YcmErrorSection', '\%3l\%8c' )
       )
     )