Activities with the same identifier are not merged correctly

[trungdong]

Two activity records in separate provenance documents have the same identifier, one with startTime and the other with endTime:

• test-activity-1.provn:

document
  prefix act <http://example.org/act/>
  activity(act:executing/1, 2022-06-21T14:42:12.898+01:00, -)
endDocument

• test-activity-2.provn:

document
  prefix act <http://example.org/act/>
  activity(act:executing/1, -, 2022-06-21T14:42:13.186+01:00)
endDocument

Merging the two documents, I expect to see one activity record with both time values present:

ls test-activity-*.provn | provconvert -merge - -outfile merged-activity.provn

However, the merge activity only has the startTime, not the endTime: activity(act:executing/1,2022-06-21T14:42:12.898+01:00,-) (the actual output from the above command line)