Mesh not identical or transfer uv maps operation error?

here are two sets of mesh which looks identical, vert edge face count and even the vert index order are the same.
when use “transfer uv maps” from 2 to 1, 1 as active object. mesh 2’s uv is messed up. vice versa.
if duplicate them and use transfer uv maps operator on their respective duplicates, ( after altering their UVs a little bit) the results work as expected.
is there any different attribute between mesh 1 and 2? or transfer uv maps has error?
here is the file[blend file]( map transfer.blend)