I have a BuildCraft quarry pumping items into a relay, then there is a filter that accepts cobblestone and dirt branching into a trash can and, after that, some chests.

The quarry is powered by an IC2 kinetic wind generator so depending on wind it is sometimes faster.

I'm finding that when the quarry goes really fast it spits a large line of single item stacks and some cobble skips the filter and goes all the way to the chests.The amount that makes it to the chests is minimal compared to how much gets deleted(some hundreds reach the chest only).

It happens for example if I manually put many single cobblestone itemstacks in the relay too.

EDIT: I have added another trashcan just in case it was having some issues with taking many items at once, it still happens

EDIT2: After some hours I found the quarry spilling items on the ground, the relay was full, after breaking and replacing the tube on the relay's output everything worked again
BluePower-1.7.10-0.1.732-universal

EDIT3: Today I have found a similar issue with a retriever, it seems to stop working after a while.It gets working if I replace the tube connected to it's input