To the stone skin spell and other enchantments going away after some number of turns, I don't think this is a bug, but instead because those spells have a finite duration, since I do remember several of the spells in the last beta had durations set instead of requiring them to be canceled. When a spell has some duration, that duration should show up in the spellbook. I also thought it would show up in the info card for the spell, but I just checked and it actually doesn't, so.... that will be added, since it's important information 
. Also, when you have an enchantment cast with a set duration, you should be able to see the number of turns left as a number over the enchantment slot in the spellcaster's "Enchant" tab. If you don't see these durations anywhere for these spells and they are still disappearing, then that would be a bug.
Just re-tested. It's gone from the enchants tab.
Also, when I over the mouse over the unit's defense to see the formula, I think spells like stone-skin should show as separate items. Even while the spell was in effect, you couldn't tell from the formula -- guess it was reflected inside something else.
The effect from stone-skin and other spells would show up in the stat breakdown tooltip in the unit's details and equipment window (what pops up when you click on their center medallion). Right now the stat breakdowns are separated into stuff your unit is getting from equipment/spells/abilities in the details screen, and then location-specific bonuses in the main map context (such as terrain bonuses and city stationing bonuses). The idea being that the former is stuff affecting that individual unit whose info you're looking at, while the latter is stuff that would affect the entire army if that unit happens to be in an army at the moment, and based on map stuff.
