The IPUMS International team has verified that this is an issue with the raw data they received. There appear to be two issues:
Duplicate records (two records that are identical in every way).
Duplicate seqm number for apparently different people. They suspect that this is mainly caused by one issue: there were only four places to list migrants on the questionnaire, and enumerators were instructed to use a second form if there were more than four migrants. They believe the seqm was then repeated for the additional attached questionnaires.
To fix these problems, the IPUMS International team plans to re-number duplicate values of seqm within a household. These will be posted on the website during the next data release. They do not plan to drop records, so there may still be a need to manually drop individuals with apparent duplicate records (issue #1).