No Lugers, except those post-WWII models made for the U.S. market, were ever marked with the caliber in a way most users would see and understand.
On the malfunctioning, I strongly suspect the ammo was poor quality reloads. The 7.65 guns are usually far more reliable than the 9mm's and are a sweet gun to shoot due to the low recoil. And the 7.65 is nothing to stand in front of; it puts out a 93 grain bullet at around 1220 fps, definitely not a joke. The downside, unless you reload, is cost of ammo. The 7.65 was never used in large quantities by either military (except for Switzerland) or police, so surplus ammo is rare.