Dear Peter,
I found some info on the incident, taken exactly from HELLENIC ARMY GENERAL STAFF - ARMY HISTORY DIRECTORATE, A history of the partecipation of the Hellenic Army in the First World war 1914-1918, Athens 1999, pages 31-35
On September 1916 Greek Army Corps D based in Eastern Macedonia, with its HQ in Kavala, was forced to surrender. It had three Infantry Divisions (5th, 6th and 7th) and some minor units, among them 7th Field Artillery Regiment. Before the capitulation, on 12th September 1916, the guns and vehicles of the 7th Field Artillery Regiment (with ten artillery batteries) were loaded onto the troop ship Ares, that sailed to Volos. Thus they were not taken over by bulgarian Army. During the voyage the Ares was forced by a French destroyer to sail to Solun. So the guns and vehicles escaped from Bulgarians had to surrender to Greek Army of National Defence, that supported the Etente. The rest of Army Corps D was massed in Drama, where Bulgarians ordered that its guns and machine guns were stored in separate buildings. But these weapons too were not captured by Bulgarian Army. Between 15 September and 27 September Army Corps D (with 16 mountain guns) was transported by rail from Drama to Silesian city of Goerlitz in germany where it was interned.
Regards
Kaan