"Merge" mode of the "Read Sequence" workflow element doesn't work

To reproduce the issue:

1. Create new schema in the Workflow Designer: "Read sequence" > "Write sequence"
2. Input two or more files in the "Input files" parameter of the "Read sequence" element.
3. Select "Merge" in the "Mode" parameter of the "Read sequence" element.
4. Set location of an output data file in the "Output file" parameter of the "Write sequence".
5. Run the schema.
=> The schema ran successfully.
6. Open the result file in the Sequence View.
!=> The result file contains only the first sequence.