This has happened to me numerous times and it makes me want to dump Magento forever.
I'll be editing a product in the Admin backend, and I spend a good 30 minutes writing up a nice long description. Then I hit save, and it takes me to the page that asks for my username and password. (Evidently my session timed out.) So I enter that info and submit the form.
Now I am taken to my default admin page and all of the changes I made to the product description do not actually get saved but instead get lost forever, costing me tons of work.
For example just now I created a whole new product and filled out all the requisite blanks and when I went to save it, I had to log back in and it retained none of my changes. I cannot work this way. It's infuriating, to say the least.
Please let me know how to lengthen the amount of time sessions last for, or turn on some kind of auto-save feature.