Inconsistent Results When Joining Tables After Adding Keys

I'm finding these two Table.NestedJoin expressions to be unequal, and I don't understand what would be causing it? The first runs much faster than the second, but that does me no good if it isn't the same result as the second…

Table.NestedJoin(
    Table.ReplaceKeys(
        LEFT_TABLE,
        {[
            Columns = {"UID"},
            Primary = true
        ]}
    ), 
    {"UID"}, 
    Table.ReplaceKeys(
        RIGHT_TABLE,
        {[
            Columns = {"UID"},
            Primary = true
        ]}
    ), 
    {"UID"},
    "SUB_TABLE",
    JoinKind.LeftOuter
)=Table.NestedJoin(
    LEFT_TABLE,
    {"UID"},
    RIGHT_TABLE,
    {"UID"},
    "SUB_TABLE",
    JoinKind.LeftOuter
)