Stuck Midi Notes sound but are not recorded - any advice?

Hi, have a strange issue here - hoping someone can give me some advice as I try and narrow down the issue.
 
I insert a softsynth into a blank project, set the midi input to my Nectar LX61 and record some playing. Occasionally I get a stuck note (Which requires either the same key to be pressed again on the LX61, or use of the panic button in Sonar)
 
So my initial thought is the LX61 keyboard is suspect (not sending an off msg perhaps) , but if I play back the recording, the stuck note doesn't happen...
 
So, does Sonar apply some filtering to what's recorded? E.g. Are only notes with a both an on and off event recorded?
 
Thanks in advance!
 
 
 

Thanks Ken - my "prepare using ...ms" is set to 1000, so have already ramped it up a fair bit.
 
Think I'm getting closer to an answer though - Looks like Sonar does filter what's recorded, as the event list only shows the note and duration (not a separate on / off message) - so guess it makes sense only notes with both an 'On' and 'Off' msg are recorded in the event list.
 
I captured some input from the LX61 using Midi-OX and then compared the number of on / off messages. Strangely, in what I captured there was an additional 'Off' msg. Can't see a keyboard sending an 'Off' msg without having first tried to send and 'On' msg - so think the issue is probably with the keyboard / cable / usb interface.