Ever since the introduction of the "new search", place names have been assumed to be in the US unless you specify otherwise. This appears to be intended to cater for the mass of US subscribers, who have only a very sketchy concept of geography.
It is only very recently that they have tweaked the place name lookup boxes to bring UK places to the top of their list when referring to UK databases.
They have also relaxed their rules on place names being used for database lookups. Previously, where a place of birth on a census sheet, say, was written, and correctly transcribed, as "Birmingham", the person could not be found, because it did not exactly match the Ancestry Gazetteer, which had the place as "Birmingham, Warwickshire, England". It still does not allow wildcards, but it is an improvement.
Some places are still not in the Gazetteer, or are badly defined, so will never be located. Tower Hamlets, for example, is claimed by Ancestry to be in Kent, rather than north of the Thames in Middlesex, so we have to resort to the "Keywords" box if we are to locate relevant records.