Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 10
Communication Breakdown; Confusion; Distraction; Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Separated Traffic
Human Factors; Procedure
I handed off Aircraft X to HTO sector.  I still had communications with Aircraft X. I had radar and communications on Aircraft Y.  I climbed a departure off of JFK to FL190 ref these aircraft.  The HTO sector changed the data block on Aircraft X to show FL190 and was handing the aircraft to the SARDI sector.  I asked my handoff if he gave control and he said no.  I called the HTO sector and asked what he was doing.  He asked for control and I said no due to traffic.  I asked him to change the data block back to FL210.  I then realized I hadn't switched communications and switched Aircraft X to HTO.  As soon as HTO had communications with Aircraft X they put FL190 in the data block and handed the aircraft off to SARDI.  I called back to HTO sector and asked if he was descending Aircraft X.  He asked me if I gave him control.  I said no and he said then I'm not descending him.  I told the HTO controller to put back the assigned altitude because I'm getting conflict alerts on Aircraft X and Aircraft Y.  He never did and I advised my supervisor.Do not change data blocks in other controller's airspace.
A ZNY Controller reports of another Controller changing the data block of his aircraft. The other Controller asks for control of aircraft and the reporter advises no due to traffic. The Controller then transfers communication to other Controller and other Controller changes data block again. The reporter asks other Controller if he gave them control and he said no. The reporter asked again for other Controller to put the correct altitude in the data block. The conflict was because of the other Controller changing the altitude in the scratch pad area.