You guys have finished what I started to say.
Once I had some broadleaf that I put away in a ziplock bag, in "low" case and it sat for about a year. When I opened it the smell of ammonia knocked me out almost. I couldn't figure it out because, if anything, I had over sweated the broadleaf and it was black and thin. After a while, it did dissipate.
I didn't mean to say that tobacco never should be stored in plastic. Smaller amounts of leaf in low case will be OK for a long time, and plastic bags are essential when shipping small amounts by mail. I have all my stuff stored in plastic bags except un-stemmed leaf which I keep in a not airtight bin with humidification packs made for humidors. And it is a good idea to check tobacco regularly to make sure it is OK. More than once I have put tobacco away that was too damp. It is a matter of "feel," something you learn by doing.
CT