Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Confusion; Other / Unknown; Human-Machine Interface
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Became Reoriented; Flight Crew FLC Overrode Automation
Human Factors; Environment - Non Weather Related
Second leg after launch from airport standby.  Short return leg from ZZZ to ZZZ1.  Basically empty jet (takeoff weight 223;000 LBS) with low level off for departure (3;000 feet MSL; 2300 feet AGL).  We had discussed and decided to leave the power setting in Climb 2 due to the low level off.   At 1;000 feet AGL the PF called for VNAV.  I pressed the VNAV button; but I believe the aircraft had already gone to altitude capture mode and did not take the VNAV selection - which I didn't immediately catch because I was busy raising the flaps as the jet was rapidly accelerating.  The FO commented that 'VNAV was doing something strange.'  I looked at the MCP and FMAs and saw that 128 KTS was the commanded speed and we were not in VNAV; however the autothrottles were trying to advance to climb power.  The PF was hand-flying and over-riding the autothrottles.  The momentary confusion and light aircraft weight caused us to miss our 3;000 foot level off.  We ballooned to approximately 3;500 feet before getting back down to 3;000 feet.  ZZZ Tower never said anything to us and switched us to Regional Departure.  They queried 'what happened back there?'  I explained that we were light and had some issues with our automation.  No further inquiries were made.Abnormally low level off with a very light jet.I should have done a better job of monitoring the FMAs when I initially pressed the VNAV button.  This would've helped me be a better PM and point out what was happening earlier.  I also don't think I was quite mentally prepared for how low the level off was and how much excess performance the jet would have at our light weight.   I think this was partially due to inexperience with this scenario and also just being a bit rusty (flown 1 time in the previous 3 weeks due to vacation).
Air carrier Captain reported the aircraft was very light weight. The pilots were unprepared for the quick low altitude level off and deviated from the clearance.