recall mode: tsv export fails to separate mention spans

[xiaoling]

For example, I labeled a few mentions

and then chose to export the labels in tsv. The resulted file looks like the following:

id label
id1 325,326,327,329,330,331,12,329
...

I also tried json format, which works fine ({..., "label": "[[325,326,327], [329,330,331], [12], [329]]"}).