I have been experimenting with using aeropress with courser grind lately and today, while preparing a cup of my blend which compose of Burundi/Tarzania in 50/50 ratio, I ran into my first major problem with the Aeropress. As usual, I'm using the aeropress the inverted way, I filled up the aeropress's chamber with more water than I suppose to and when I stir the slurry, some of the coffee ground and water spilled out. These coffee ground which are courser than what I used to use before got stuck to the interface where one would engage the black filter holder.
As a result of this, it was impossible to get the filter holder to engage into the main aeropress chamber because the spilled course coffee ground is in the way. I ended up spending more than a minute trying to twist the filter holder in; with a lot of cursing and torque, it finally engaged but I ended up letting the coffee brewed for way more time than it should. The resulting cup didn't end up very good but because I was using very course grind, it wasn't horribly over-extracted. For a moment there, I was considering dumping the whole thing and start over again.
So the moral of the story is, if you are going to use the Aeropress by the inverted method, do not top off with too much water, and make sure you do not stir so vigorously that coffee ground are spilled out, otherwise you might end up ruining your cup of coffee.