The limitation to 5 active skills is intentional. If you could activate magelight, then switch to other weapon bar without it deactivating, you would essentially have six active skills instead of five.

You need to figure out which 5 skills work best for you, then use those. It may make magelight useless for your uses, but someone else may have other priorities and use magelight in one of their configurations (for instance when he knows there's a nightblade lurking nearby)

Think about it. If you could have magelight up at all times without having to sacrifice one of the five slots for it, then the ability would become mandatory for PvP, and it would essentially render all stealth in the game useless.

Or in other words, the only reason why stealth is still useful with magelight available to everyone is the fact not everyone will be willing to sacrifice the slot for it.

Thanks for your replies guys.
The thing about mage light sounds sensible. But my objection is that even though it's not on the weapon bar I have active, it's still slotted.
I have it on one bar, activate it, and change bars, and it should remain active.

For instance, the sorcerer spell Lightning Form has a 6 sec duration (more if you morph it). So, if you use the ability, which you have slotted in one action bar, then swap bars, does that cancel Lightning Form?

It seems to me that it doesn't. A huge difference between Lightning Form and Mage Light is that the first is on a limited duration while the second is toggle on/of.

I'm running heavy armor as sorcerer, and have one setup for ranged and one for melee.
For ranged setup I use the heavy armor skill Immovable for defense. It costs stamina, so I can keep my mana for nuke.
As melee I use Lightning Form for defense. It costs mana, and I use stamina for 2 hander attacks, along with a few instant cast sorcerer spells in the mix.

But, on rare occasions I need mad defense, and then I pop both Immovable and Lightning Form, and it does seem that I get both buffs even though I have one on each action bar.

Any skills that are toggle on/off will only stay toggled on if you have it on both weapon loads. This works the same for things like the mages summons.

Skills that you cast and have a set duration will persist through weapon swaps for their full duration.

This is how ZOS intended it to work.

Like I said in another thread why not "remember" what was toggled, so when you change the toolbar back it comes back. It would be the same thing that happens to summons when you go into the water, they go away (the 10% penalty remains) when you come out of the water it shows up again.

It could be the same with skills that can be toggled. Summons/effects go away, keep magicka penalty on (since summon/effect still active), switch back and summons/effects go back. Seems fair and simple to implement since it is already used when you go into water.

When you toggle you activate your ultimate you choose different set of active skills . whilst ultimate is active choose k menu the drop the active abilities in to the slots that you want to use with your ultimate skill. If you are using bound or summoned familiars and want to continue using them whilst ultimate is active they must be in the same slots as when your normal weapon slots are active i.e ultimate is not.