Currently there is a bug with favored soul and spirit shaman where you continue to gain spellcasting progression if you take an arcane progression prestige class.
Long story short (medium): when OEI added the new classes that advance arcane progression for MotB/SoZ they didn't add entries to the cls_featmap_xxx files like they should have. Those files control who gains progression if they have a certain feat. Since Favored Soul and Spirit Shaman were NOT in those files (so it was neither a -1 like it should be or **** for no entry) my belief is that the OEI code threw an error or fell through a switch statement to the default case which was full progression. That's why you could get full progression with sorc, fs, and ss all with a single prestige class.
Thankfully all of the divine featmaps had to be updated for these two new classes so they had the fixes (except for the hellfire warlock stuff and the doomguide).
Longer story short: the new featmaps I've done include *all* of the progressions for all of the caster base classes. That means no exploit is possible regardless of what prestige class you take.
Existing characters who exploited will suddenly find themselves with the correct number of spells as the engine seems to throw out the invalid ones now that it can correctly calculate how many you should have. This worked for me with the OC but may have issues with a PW that is running with ELC turned on.
Below are two downloads which contain the fixes. One for just the OEI content and one for both my content as well as OEI's.
10 - A Masterpiece, Genuinely Groundbreaking 9 - Outstanding, a Must Have 8 - Excellent, Recommended to Anyone 7 - Very Good, Deserves a Look 6 - Good, Qualified Recommendation 5 - Fair, Solid yet Unremarkable 4 - Some Merit, Requires Improvements 3 - Poor Execution, Potential Unrealized 2 - Very Little Appeal 1 - Not Recommended to Anyone