In ECLWatch, open workunit details for a running workunit (i.e., one the browser will auto refresh). Click on "ECL" subtab and browser tab will close without warning or complaint (no pop-up or other error reported).
There may be other tabs that act similarly. Also, going directly to said workunit via the "pop out" link provided (e.g. http://<esp-ip>:8010/?Wuid=<wuid>&Widget=WUDetailsWidget#/stub/Summary) acts similarly if workunit is still running.