In the file below, Offset each curve individually to the outside with a value of 3 and Corner=Round. Works correctly. Undo the offsets and then select both curves and run OffsetMultiple with the same values (single offset). The red curve makes an open offset curve instead of a closed one like normal Offset does.
V7 OffsetMultiple appears to handle this case correctly.
BadOffsetMultiple.3dm (2.1 MB)