BUG: deep copy is needed for the result of cast filter
Revert "STYLE: remove no-op"

This reverts commit 4d0db7c6a3ad0e451b48ee58458b31db94b0e1bf.
Revert "BUG: hacks to work around the problem of label map not being updated while editing"

This reverts commit 70f61449e983d8b9896a7a240d1db34c4f28ee71.
Merge branch 'label-refresh-bug'
STYLE: no need for extra observe