All my attempts as a kid to use canned shellac were failures .Same thing for friends and family. Canned shellac is responsible for myths about real fresh mixed shellac.
In fairness Zinsser figured out some tricks to stabilize the shellac to a degree that hadn't been achieved before. I read their patent once, but I've forgotten the details.
I did have one can do this a number of years ago...it was nearly empty and had been hanging around for awhile. I forgot it and left it in a place I shouldn't have. That's been the only incident, however...I use the stuff quick enough that even if it is hungry for steel cans, it doesn't have time to have its meal.
I had one leak only a few months after the production date. I guess some batches are hungrier than others, or some cans are worse than others.
I am with Ted and Mel on this all the way, keep your shellac in dry form and mix it up with alcohol of your choice as long as it is minimal 96%. Store the mixed up in glass with a cork stopper and dilute it, maybe even 20:1 every time you use it.