Hi Omar,
Thank you for using Syncfusion products.
I am afraid that I could not able to reproduce this issue at my end.
Could you please try to reproduce the issue in the below sample ?
http://websamples.syncfusion.com/samples/Tools.Windows/F62538/main.htmIn the above sample, custom collection is bound to bindingsource which in turn bound to MultiColumnComboBox.
Also let me know the Essential Studio version you are currently using now.
Regards,
Jaya