The issue is reproducible when the `AllowCustom` parameter is set to `true`.
Typing rapidly in the input field of the MultiColumnComboBox component causes the entered text to blink. Also, some of the inserted symbols are cleared.

Reproduction (if bug)

Open this demo: https://demos.telerik.com/blazor-ui/multicolumncombobox/custom-values

Try to input text rapidly into the input field.

from this screenshot from the demo selecting a value via the keyboard leaves the box blank

to replicate press the down arrow when MultiColumnComboBox has focus