Abbeyman

Hello, I'm flying an Wilco Airbus 320 CFM and try to get a flight done the last couple of days (EDDH/EDDL). Plan is to cruise at FL230. But the bird stops climbing at approx. 7,000 ft (in managed mode) and hangs up at that level. In selected mode he starts flashing yellow at the altitude indicator bar in PFD, showing "open climb" in the FMA and ignoring my wish to climb to a higher altitude. I have carefully programmed the FMGC and there are no altitude restrictions given. The flightplan has been entered manually and correctly. Cost index is 50, FLEX temp set to 50. I manually take off following the FD but I have to be cautious as the A320 doesn't speed up to more than 160 kts. Thus the climb is lame as I have to balance between speed and climb rate. The plane follows correctly the lateral flight plan but not the selceted altitude. I checked the internet but didn't get any answer that helps me. Is that a bug? Or what do I wrong? Best regards from Hamburg, Jan