diff --git a/invesalius/data/coordinates.py b/invesalius/data/coordinates.py
index 4eb2a61..b514c99 100644
--- a/invesalius/data/coordinates.py
+++ b/invesalius/data/coordinates.py
@@ -19,7 +19,6 @@
 
 from math import sin, cos
 import numpy as np
-import queue
 import threading
 import wx
 
@@ -35,11 +34,14 @@ class TrackerCoordinates():
     def __init__(self):
         self.coord = None
         self.markers_flag = [False, False, False]
+        self.previous_markers_flag = self.markers_flag
 
     def SetCoordinates(self, coord, markers_flag):
         self.coord = coord
         self.markers_flag = markers_flag
-        wx.CallAfter(Publisher.sendMessage, 'Sensors ID', markers_flag=self.markers_flag)
+        if self.previous_markers_flag != self.markers_flag:
+            wx.CallAfter(Publisher.sendMessage, 'Sensors ID', markers_flag=self.markers_flag)
+            self.previous_markers_flag = self.markers_flag
 
     def GetCoordinates(self):
         return self.coord, self.markers_flag
@@ -232,7 +234,7 @@ def PolhemusCoord(trck, trck_id, ref_mode):
     elif trck[1] == 'wrapper':
         coord = PolhemusWrapperCoord(trck[0], trck_id, ref_mode)
 
-    return coord, None
+    return coord, [False, False, False]
 
 
 def PolhemusWrapperCoord(trck, trck_id, ref_mode):
diff --git a/invesalius/gui/dialogs.py b/invesalius/gui/dialogs.py
index 2f408a0..aa4b5a9 100644
--- a/invesalius/gui/dialogs.py
+++ b/invesalius/gui/dialogs.py
@@ -4691,7 +4691,8 @@ class SetNDIconfigs(wx.Dialog):
         btn_ok = wx.Button(self, wx.ID_OK)
         btn_ok.SetHelpText("")
         btn_ok.SetDefault()
-        btn_ok.Enable(False)
+        if not port_selec:
+            btn_ok.Enable(False)
         self.btn_ok = btn_ok
 
         btn_cancel = wx.Button(self, wx.ID_CANCEL)
diff --git a/invesalius/gui/task_navigator.py b/invesalius/gui/task_navigator.py
index 127bcab..2a4db1c 100644
--- a/invesalius/gui/task_navigator.py
+++ b/invesalius/gui/task_navigator.py
@@ -1379,7 +1379,7 @@ class MarkersPanel(wx.Panel):
 
         next = self.lc.GetFirstSelected()
                
-        while next is not None:
+        while next is not -1:
             selection.append(next)
             next = self.lc.GetNextSelected(next)
 
@@ -1566,8 +1566,9 @@ class MarkersPanel(wx.Panel):
         if index:
             if self.__find_target_marker() in index:
                 Publisher.sendMessage('Disable or enable coil tracker', status=False)
-                Publisher.sendMessage('Robot target matrix', robot_tracker_flag=False,
-                                      m_change_robot_to_head=None)
+                if self.tracker.tracker_id == const.ROBOT:
+                    Publisher.sendMessage('Robot target matrix', robot_tracker_flag=False,
+                                          m_change_robot_to_head=[])
                 wx.MessageBox(_("Target deleted."), _("InVesalius 3"))
 
             self.__delete_multiple_markers(index)
--
libgit2 0.21.2