" I'm in the northern hemisphere, so perhaps things are different here, like with toilet swirl direction? smiley-grin "
I think you are on to something there, we get the leftover toilet grade celphones down here 
I was involved with scrolling advertising machines in University cafeterias for some years , and the original method of sensing the end off each poster had a coil near the edge of the poster, and some metalic tape on the back of the poster where it should stop. ( it looked really horrendous )
Whenever they complained about the poster stopping half way, the tech would go out after hours and all was fine, so I went there during the day , and all the students were messaging on their phones at the tables around the scrollers !
I changed it to an optical system and it was fine.