Just wanted to share how I fixed the problem with Lines disappearing in Bitmap Layers after 5-7 seconds. This happened after upgrading to SBP 4.1 from SBP2.
The Problem :
I would draw something and the line appeared on the Stage View and then disappear after 5-7 secs. The lines could still be seen in the thumbnails.
After playing around in EDIT - PREFERENCES - ADVANCED - I found that the problem was caused by ((( Enable Mipmapping on Bitmap Layers ))). After turning this off the problem went away.
Strange that in the 30 day trial this was not an issue.
Anyways, there you have it in case you run into this problem. I am running Windows 7 ATI RADEON HD 4600 Graphics card.