Hi Natalia,
Thank you for using Syncfusion products.
In ComboBoxAutocomplete control , the combobox drop down is overridden for showing the autocomplete dropdown . So instead of adding items to the items collection, add items to the autocomplete control using its DataSource property.
The following code snippet illustrates this.
[C#]
comboAutoComplete.AutoCompleteControl.DataSource = strcollection;
Please find the sample below that demonstrates this.
http://files.syncfusion.com/support/Tools.Windows/7.2.0.20/56844/main.htmPlease followup the incident 56844 for further queries.
Regards,
Jaya