It should definitely be saving in the trial version.
Here are some things to check:
1) Are you pressing the "All" button at the top of the recipe box to see all the recipes in the box?
2) Is the folder that your "My BigOven Recipes" folder is stored in marked read-only, and/or does it grant your Windows account full read/write permissions? It should allow you to write files to it.
3) Putting aside importing recipes for a moment -- can you create a new recipe in the Standard recipe box by using New Recipe on the toolbar -- entering the information. Will the recipe persist when you open the program again? It should. If not, there's something blocking BigOven from saving it to your folder.
4) Do you have an apostrophe in the recipe box name or filepath? (e.g., Find the location of the recipe box on your PC and look at the full filepath. Make sure there are no apostrophes in this filepath.)