I had that happen to me once also.. I had the brain fart to top up the reservoir, but the lift wasn't completely down, when I did lower it, I had the same air filled hydraulic fluid overflow as you have...
__________________
87 930 GHL/Rarlyl8/Garretson/GT3582R/1 Bar/Wevo shift, mounts/Meth inj/LM-2/Custom Fuchs/Carrera intake manifold/Xtreme Carrera heads P&P/3.4/DR 993SS cams/ Mahl/Pauter/JE/Niresist/ARP/twin COP/8.25:1/KEP stage 2/twin tials/close 2,3,4th. MS3Pro Evo
500+ HP, BTSOMP Dyno