We have a simple list with a Lookup to another list on a single-line-of-text field.
I customise the form with InfoPath and change the drop-down-list to Combo Box. I set the List ID as the Value and the List Title as the "Display Name". When I test the form and start typing in the Combo Box the type-ahead (custom text / pre-fill / suggestion ) feature doesn't work properly. For example, if I paste a valid value I get the error "Only positive integers are allowed".
It's as if the Combo Box is forcing you to use the mouse to select a valid value and the auto-suggest (and paste) simply doesn't work.
Funnily enough, the paste seems to work in InfoPath Preview Mode, but not in Run Mode (via the Browser).