It's difficult without knowing the system equipment layout but we'll have a go...

Cooling Mode -
Outdoor unit - Solenoid valve - pipework - indoor unit EEV - indoor coil - pipework - outdoor unit.
Indoor EEV has liquid feed from outdoor unit and expands liquid into the indoor coil.

Heating Mode -
Outdoor unit - pipework - indoor unit coil - indoor unit EEV - pipework - outdoor unit solenoid valve.
Hot gas runs through the indoor coil before being arrested by the EEV. EEV may not have a liquid seal on it so will bleed vapour.

Short pipes have not provided sufficient resistance to the hot gas so coil operates at higher pressure/temperature.

I could be wrong though.