hi niner
i can't address most of your post, but i can comment on two items.
there is no fix for the explored areas to quickly become as they should be - explored...but you needn't (usually) re-explore/re-walk. simply take your cursor to the edge of your monitor (thus scrolling land area) and let it go. this saves a lot of time walking as the areas are really not covered again by the fog-of-war.
second. sometimes in battles you'll find yourself suddenly with a black screen except for the character portraits in the top right corner. if this happens, double click on one of the portraits, it'll re-center (or clear. not really sure which is taking place with this bug).
remember to click the 'group' button again.
hope this helps. the blackened explored area thing happens primarily in the BFs and if you look close at your map you'll see it's not the graduated fog-of-war black, it's straight lined rectangular boxes.
