Day Trader’s Weekend Aftermarket Lounge 1-3 Feb 2019, page-27

Hi All
I had an issue on Friday arvo and was wondering if anyone out there  has experienced something similar.
Im in the process of changing brokers(CommSec to CMC) and transferring my existing holdings over.
On Friday I decided I needed to lock in some profits on a particular share I was trading. Went into my commsec app, pressed sell and was taken to the order page where it clearly stated “ 50000 units available “ so I sold some for a cheeky profit. About 10 minutes later I get a call from commsec telling me my shares are in the process of being transferred and that now I have to buy them back on Monday morning first thing. Have I been a bit of a banana here? Or should they have really made my shares “unavailable “ on the order screen?
Thanks in advance