Reproduction steps:
Submit a cmdline job (e.g. sleep 240), on (say) 3 CPUS.
Right-click on the job, increase to 5 CPUS.
Job doesn't change number of CPUS
qbmodify the job via the cmdline, and it works fine.
Note that in the job history, there's a "modified" history event (from the GUI) that lists everything: priority, name, cluster, restrictions, requirements, reservations, groups, hosts, cpus - but nothing changes.
The subsequent "modified" history event (from the cmdline) only shows "modified: cpus".