Steps to Reproduce

run the attached example

click the buttons in order
1.1 "listen" A, B, C, "fire"
1.2 "unlisten" C, B, A , "fire"

2.1 "listen" A, B, C, "fire"
2.2 "unlisten" A, B, C , "fire"

Actual Result

1.1 console shows

onAnyWatch A p1
onAnyWatch B p2
onAnyWatch C p1

1.2 console remains empty (expected)

2.1 again console show the expected listener invocation

onAnyWatch A p1
onAnyWatch B p2
onAnyWatch C p1

2.2 listener A on P1 is still called correctly

onAnyWatch A p1

i.e. it wasn't removed even though unlisten was called

Expected Result

zWatch.unlisten should remove the specified listeners correctly

Root Cause

the mechanisms how listen and unlisten determine where to add/remove a listener don't match

listen: will create duplicate entries for the same widget if another widget has been added for the same bind level inbetween
https://github.com/zkoss/zk/blob/v8.0.4.1/zk/src/archive/web/js/zk/evt.js#L468-L471

unlisten: will only try to remove the listenerinfo from the first element found
there's no check whether or not the $remove function was successful
https://github.com/zkoss/zk/blob/v8.0.4.1/zk/src/archive/web/js/zk/evt.js#L500

Workaround

replace line 500 in evts.js with the below to continue searching for a matching listener if $remove returned false

	if(!wts[j][1].$remove(inf)) {continue};

An alternative fix could be to make sure all watch listeners for the same widget are added in a single listener info object during listen, however this will affect the listener invocation order.