If a changelist is specified in scm: checkout, p4 polling does not work. The result is the specified changelist is used in the range:
P4: Polling with range: 53910841,53910841
p4 changes -m20 //clientname_/...@53910841,53910841
This result, is polling will not detect any subsequent changes.
If changelist is not specified during scm: checkout,
P4: Polling with range: 53910841,now
p4 changes -m20 //clientname_/...@53910841,now
P4 plugin should always use "now" for the higher end of the range, regardless if a changelist was specified or not.