System Field no longer has search capability

A few of my users recently pointed out that the Vendor field on the Purchase Order form changed from a searchable field that would allow users to narrow selections by keywords to a more traditional dropdown that only goes by the leading characters in the list.

To put it another way, previously if a user wanted to find 12345 ABC Company in the Vendor list, they could have typed 12345, ABC, or Company, and the controls dropdown would have filtered accordingly. Now, they can only use the leading characters (the Vendor ID) to narrow their selection, which is less user friendly in cases where they can recall the vendor name but not the ID. To contrast, another field on the form of the List/Record type still exhibits the desired behavior. This field, which we use to select an associated project, has "<Type then tab>" as placeholder