In these two passages, there were originally six cases of “to build up”, but in two cases the up has been accidentally lost (one case was in the 1841 British edition, the other in the 1830 edition). These changes are not due to any kind of systematic editing, but they have nonetheless persisted in the LDS text. In the second case, the 1908 RLDS edition restored the original up to the RLDS text. Obviously, the tendency to drop the up is quite strong. There are other places in the text where up has been omitted; for some examples, see under Alma 2:15.
Summary: Restore the missing up in Ether 13:5 (“and it should be built up unto the house of Israel”) and in Ether 13:8 (“the remnant of the house of Joseph shall be built up upon this land”).