Update ckeyon.rst

Noe 2 added on behalf of PJW.

sphinx/source/C/ckeyon.rst

@@ -4,7 +4,7 @@ CKEYON
 ======
 
 +----------+-------------------------------------------------------------------+
-| Syntax   |  CKEYON                                                           |
+| Syntax   |  CKEYON [#channel]                                                          |
 +----------+-------------------------------------------------------------------+
 | Location |  Pointer Interface (v1.23 or later)                               |
 +----------+-------------------------------------------------------------------+
@@ -15,3 +15,28 @@ See :ref:`ckeyoff`.
 
 There were problems with this command prior to v1.56.
 
+**Note 2**
+
+At some point CKEYON started to have to take a channel number, ie
+CKEYON #channel.
+
+If you dont give a
+channel number the commands try to open their own channel - that hybrid
+number 0/1, as do a number of IO commands (at least in SMSQ/E). All well
+and good. But if you, say, open your first channel as number 3, as happens
+automatically if your first channel in a daughter SBASIC or Qlib compiled
+job, and you open it with ch = FOPEN("con_") then, if that channel is
+OUTLiNed to be smaller than the default channel, the call fails and returns
+to the routine - which gives up. But doesnt say anything! However, now
+there is dangling, open channel in the main channel table that SBASIC
+doesnt know about. So next time you use this command yet another channel is
+opened in the main channel table! And so it goes on ad finitum until the
+job is killed - or the system chokes.
+
+This is a rare circumstance, admittedly, but it is still a bug.
+
+
+The bug fix is that
+if the circumstances described pertain, the call will return with an Out of
+Range error.
+