It seems to only happen when "angled" inserters are used (like those provided by the Side Inserters mod) : This can be easilly reproduced with this blueprint:
Code: Select all
{
{
entity_number = 1,
name = "inserter",
pickup_position = {
x = 1,
y = 0
},
position = {
x = 0,
y = 0
}
}
}