Some region codes are integers, some are strings

[stuwest]

In territory array keys, region codes with leading zeros are parsed as strings but those without leading zeros are converted to integers:

[stuwest]

Turns out this is a "feature" of PHP's loose typing see the PHP manual on key casts that happen in arrays:

Strings containing valid integers will be cast to the integer type. E.g. the key "8" will actually be stored under 8. On the other hand "08" will not be cast, as it isn't a valid decimal integer.