I really enjoy this game, so i'll actually post about the bugs and problems I have found in hopes that they will be remedied and make a good game even better. These are all present in version 1.3 for me.
1. Already mentioned, but of HUGE importance is the
Ring and Trinket stacking issues I only wish i could put on half of these items i have found, but unfortunately the game won't allow it. It takes an act of divine intervention to even get 4 rings on and it's completely impossible to get 4 rings you'd want on period, simular issues with trinkets, jus 2 slots there tho.
2. Quest log bugs with the wizards letter and Shadow ruins quests not clearing when complete.
3. There needs to be something to prevent a person from entering the trials without having talked to the apothacary first so she kills her husband. My bro neglected to talk to her first, beat the trials and recovered the artifact from fathian manner. Then he went to buy stuff from her an she rewarded him for finding her son, then killed her husband and locked up shop permenantly. This in turn killed his game much later on because for some reason Maya (?) wasn't there to meet him at the ruins when his quest log said to go there an meet her. He wound up deleting that character an starting over after days of backtracking to try an find the missing link, the apothacary glitch was all we could find wrong.
The shadow ruins entrance bein a 1 time thing is pretty lame too, especially when a monster knocks you into the teleporter when you are no more than 2 steps into the place

in my opinion the gate should remain open until the boss is defeated and his hold over the mortal realm vanquished.
4. This one isn't really a bug, more of a funtionallity issue. They Buying system is way too cumbersome. The stock window is on the right side of the screen while the buy window is over on the left. when you have to buy tons of nether components this setup is not Carpal Tunnel Syndrome friendly.

The solutions would be have the buy amount window pop up over the item you clicked to buy or just make both the windows floating so players can put them where they want them.
Also related to the buying system is the limit of 10 items. This is really really lame when working on nether spells that you need a lot of. Patially cuz of the mundane clicking over an over an over an over and also because of the cumbersome buying menus. Since you can sell thousands an thousands of stackable items at a time, why are we limited to buying in 10 lots? Please up the # of items purchaseable in one transaction via the slider or allow us to enter in how many items we want to buy numerically or something cuz my mouse and wrist can't take much more o this
5. Some of my higher end nether spells cast hit or miss (i have plenty of nether skill ranks to cast them), mostly Summon Deathlord and Summon Fiend seem to be flakey, especially in dungeons. The lvl 10 spell Hatred isn't working at all for me
I'll post more as i find it, i am sure there are some other things that i am just not remembering at the moment.