Shellac, once mixed with alcohol, gradually degrades (process is called esterification) to the point where it won't ever harden. Ever. Some pre-mixed varieties (e.g., Zinsser Seal-Coat) guarantee up to three years from date of manufacture (but it might have been sitting on the store shelf for 5 years). I've used it successfully after 4 from a can that got hidden on the back of a shelf. Home-mixed can go bad in as little as 12 months, but I start testing after 6. The way to test is to put a puddle on some wood. If it's not hard the next day (shellac usually dries in 30 minutes), it won't ever. Poor storage conditions (heat) accelerate the process.

Here's how to break the code that tells you the date of manufacture: http://www.popularwoodworking.com/woodworking-blogs/flexner-on-finishing-blog/user-unfriendly-zinsser-bulls-eye-shellac

As for your current problem, I'd wipe it off with a rag wet with denatured alcohol, stripping off the bad stuff. Let it dry and recoat with fresh shellac. Waxing does well on shellac, so you can do it once cured. Shellac also has a relatively high moisture vapor penetration coefficient, so should help the swelling, if that indeed is your problem. It could just be the shellac sticking and gluing itself together.

Wow, good to know, thank you! I used Zinsser.

So, wet a rag with denatured alcohol, wipe down, and that'll remove what's turning sticky?

Yes, swelling is not the problem, it's the shellac gluing itself together.

Thanks again!

Yes, alcohol will re-dissolve the shellac. Keep turning the rag as it gums up.

good shellac will dry hard and not stick to itself. Probably indicates old, bad batch of shellac. I would try steel wool and paste wax before stripping it off.

I 100% agree with uncle Bob,paste wax applied to intire surface is burning the bridge behind you. If there's a sticky drawer after every thing is dry,rub a candle along contact surface.