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We are currently analyzing the reported behavior with SfComboBox using the provided scenario. We will check and update you details on 12th Dec 2019.
Thank you for your update.
Query : I've been working on this problem and have found that the behaviour does NOT happen when I clear() the list which is used as the datasource for the sfcombobox. The behaviour only occurs when I set the list = nothing, instead of using list.clear().
When the ItemSource has been cleared using clear method, the item would be properly removed. So we recommend you to use the clear method.
Query : To stop this behaviour I've had to set sfcombobox.autocompletemode = none, then fill all the sfcombobox.text fields from a database record, then set autocompletemode to suggest/append. Is there a better way to stop the dropdown happening when the .text property is set by the code?
We are currently checking this behavior at our end. We will check and update you the details by 13th Dec 2019..