Export/rendering differences with GPU acceleration on or off

I have been having a number of issues using PPro CS5 with and without the GPU accelerated rendering. Most issues infact when the GPU acceleration is turned off.

The first issue I would appreciate some input on is the export quality of a photo or video clip when rendered/exported from a high definition project. Easiest way to see the issue is with a photo (scaled in Photoshop to 1200x950) and simply exported as a jpg with GPU acceleration on and off. The jpeg exported using software rendering is soft (even using Maximun Render Quality). Then without doing anything I select the GPU acceleration and export as a jpg again and the image is crisp.

http://muvipix.com/cpg/albums/userpics/10003/Comparision.jpg

In the example there are crops from the exported jpgs, actual size. The top left crop is with GPU acceleration, bottom right without.

My graphics card is a GTX 260, running Widows 7 on an Intel Quad core.

Other issues I am seeing is that if I work with GPU acceleration on and then export with GPU acceleration off I am seeing differences in the exported clips from what I see in the monitor during editing. For example if I create a "reflection" of a clip it's position will be different if GPU is on or off.

I sometimes need to export with the GPU off because with complicated edits using multiple effects and tracks I get an error messaging saying the graphics card has lost communication with the driver and rendering stops. In this case I export using software rendering and the resultant exported clip not as I viewed in the monitor during editing.