2 exchanges confuse pricing

I just don't get how it works. Here i am looking at the nab trade screen that says there is 128000 shares on offer , You would think that if you bought them then they would disappear off the screen or at least register ; but no . with Nab Trade they might trade them with either exchange but only the ASX shows up and then 128000 are still on sale . this means that buys & sells are not what they seem. On asking whether there was anywhere you could monitor the other exchange i was informed by Nab Trade this was not possible ........mm