i too have the 'cano. and from my years of experience this is a normal occurrence, and yes, sometimes you do get some blowback into the bag, but this can be avoided. I personally don't mind some, it happens, but if it concerns you then maintenance is your best option. First buy replacement bags, and screens. Then invest in some alcohol and a good cleaning brush, like a kids toothbrush.

Since the screens are metal, they have a tendency to bend, and when they bend they end up with gaps that allow those small particles to invade your bag and valves. Second, the whole unit heats up pretty good, and the metal is typically cold to start with so lots of hashish resin gets coated on everything the smoke touches, this buildup gets sticky and small particulate build up in the goo, and once its heated the goo is more liquid so bits can fly back. And some people are just stupid and forget to put the tree piece in the crucible, causing leafy bits to get stuck and sucked up, big mess.

But everything is alcohol safe, so unscrew the bolts from the tree piece to take the screen and the two washers off, remove bag and rinse for hash, or discard, unscrew the top of the bag assembly, and really just break it all down to the bare nuts and bolts, give a good soak in some alcohol and you have clean pieces.
If your screen is bent, replace it, change your bag, and make sure to scrub all the pieces where it is sticky, like the tube that runs to the bag, unscrew the metal part out of the crucible and really get all the cracks where the two pieces join together.

After that, reassemble, and remember to try to keep the leafy bits between the screen, none around the rims, this lets it past the screen, clean it often to avoid that build up, soaking is all that is really needed most of the time.

Also, that liquidy resin that builds up really is a hashy oil so wipe it out with papers and vape that, but it does build up where you cant wipe it out, and sometimes globs can blow through and out, but typically its small, and its hash so no worries. I typically never worry about it though because your throat and mouth catch most of all particles before they get to your lungs, but you can keep the heat lower to keep from drying the buds into dust.