If you equip on a Necromancer an item with + to summon skeleton/skeleton mages/wraiths etc the number of minions allowed is calculated from the base not from the current number
For e.g. I have a chest armor with + to summon skeletons. I should have 8 because I have the grave walkers, marrow walkers and hallow walkers skill modifiers enabled but the maxim number of skeletons I can summon is 4. This is not just a visual bug as summoning a new one substitutes an existing one
still an issue on the latest patch. You have to remove the points and gain the xp again to spec it back in order to get the correct number of allowed summons again
skeletons are max 3. with the three nodes you have a max of 6, and then more with passive nodes and uniques. +skill affixes do not give more minion summons, they give skill points in that skill.