I happened to notice something unusual last night. Returning to town, Rosina was skirting the city walls for a few steps and she disappeared for one instant in the location shown in the picture below. She reapeated the experiment 4-5 times and there are two spots in the same area where it looks like she is stealthing for just a moment:
On a separate subject, there is one instance which I am unsure of (whether bug or intended): this concerns Bone Mages - it seems they totally cancel, with their weakening, any strength boost you may have given yourself. I make it clear with this example:
Rosina has a natural strength of 56, which boosted by the spell rises to 73. If a Bone Mage weakens her, the strength goes down to 39, no matter whether at the time of suffering the BM spell she had her normal strength or the boosted one.