columns with unequal length when outer join involves DataValues

[staples6]

See reproduced error below:

using IndexedTables, DataValues

x = table([1, 2, 3, 4], [11, 12, 13, 14], names = [:a, :b], pkey = :a)
y = table(DataValueArray([1, 2, 5, 6]), DataValueArray([15, 16, 17, 18]), 
               names = [:a, :c], pkey = :a)

z1 = join(x, y, how = :left) # this is an error
z2 = join(y, x, how = :left) # this is ok
z3 = join(x, dropna(y), how = :left) # this is also ok