I don't know about anyone else but I've spent most CC's running around with my inventory screen open (especially when I'm running torches) out of necessity (barrels poping in, torches etc.) A few observations:
An item that spawns into your inventory often moves other items even if you have empty space already.
Sometimes an Items decides it "likes" one of your tabs... there's no rhyme or reason, if your teleporter likes tab 3 and you drag it to tab 5 with your other cove stuff, then place it, the next time you pick it up it will go back to tab 3 EVEN IF YOU FILLED THE EMPTY SLOT on tab 3 trying to keep that from happening.
This can be reproduced 100% of the time while crafting, buy a trinket, it pops into tab 4 drag it into tab five, upgrade it, poof it's back on tab 4 (even if you close all the slots on that tab it will push stuff off that tab)
Sometimes items go to your first tab, sometimes your 3 tab, sometimes your 5th tab (or any other) no rhyme or reason, doesn't seem to matter where you have empty space. This of course is made even worse when you swap weapons or clickies or gear. I like to swap to GUDB. for cove skells, and then holy burst PG icy burst for hobgoblins... that causes mass inventory shuffling.
I would like to ask with the Devs to improve this... I've never seen a commercial RPG or MMO with an inventory setup this bad...
We've had Dev interaction with Phax and Madfloyd about the "random shuffle" inventory system, and both of you guys said you would look into it... You guys have even asked us for ideas, and we recommended (pretty unanimously) a "lock in place" feature that would let those of us who want to, choose to lose a couple slots to permanently reserve slots for gear that is in it. So it stays where we put it.. Please try to at least put in something that forces items to go to an EMPTY slot, and let us voluntarily reserve slots for weapon sets and gear swaping. Honestly I would gladly give up 6 or 8 slots to keep my weapon sets and items on the same page. And people who don't care can just not use the option. No one losses.