--- a/slotUI/freeslot.py	Sat Dec 21 14:54:21 2013 +0100
+++ b/slotUI/freeslot.py	Sat Dec 21 16:21:06 2013 +0100
@@ -125,7 +125,11 @@
             self.com.readline() # clear to next linefeed
             line =  "RW:%i:%i:%i:%i:%x\n" % (slot, track, sender, status, clk)
         self.log.write(line)
-        return line
+        if line.find(chr(0)) == -1:
+            return line
+        else:
+            self.log.write("malformed RX\n")
+            return ""
 
     def query(self, msg):
         if self.com: