I ran across this issue a few months ago on my -14A and it has stopped me in my tracks. Per the plans, you countersink through the spar and into the hinge leaving a knife edge in the spar. I contacted Vans and was told this is correct and they've been doing this since the beginning and that there's never been any problem with it. So far.
I wasn't happy with that answer. My day job is aircraft structural analysis for the big B. This is a condition that is not acceptable because it gives you an initial flaw for a crack to start growing. In the GA maintenance world, it's acceptable to countersink to the bottom of the first layer in the stack-up but you must stop there.
My concern is with the "never been any problem with it" statement. Has anybody ever inspected this location after a while in service? How would you inspect? The only viable method I know of that's affordable to the EAB crowd is dye penetrant. However, you need to have the crack grow to the edge (in the spar, which is sandwiched between the skin and hinge) before this method will detect it. You can also use low frequency eddy current to inspect the spar through the skin, but the training and equipment to use this NDI method costs more than most can afford.
Because I'm cursed with way too much knowledge on this particular subject, I've decided I can't live with the status quo. I'm going to have new spars made for the tab and elevator out of 0.050 in. sheet. I talked to a local metal bending shop and it'll cost about $300 to duplicate these parts. And yes, I ran this idea by Van's and as long as I maintain the proper control surface balance I'll be OK in terms of flutter.
Now before I get jumped on, I'm *not* saying this is a design flaw. Van's is probably right that it will never be a problem. You need three things for a crack to grow: 1) an initial flaw (got that), 2) sufficiently high stress (probably not), and 3) enough cycles to grow the crack (probably not with these aircraft).
For me, being the very conservative type, I'm unwilling to live with this. It'll be in the back of my mind every time I fly. It's all for my peace of mind.