When I export a horizontal bar graph as a TIF file, or copy and paste on the clipboard, I lose text on the left axis labels.

We will fix this bug in the next release. But it is easy to work around now. Use the text tool to enter some text to the left of the axis labels. Then use the "Format.. Text.." command to make the text white (or match the background color) so it is invisible. Or just enter a space. When Prism exports, it includes all objects on the page, even those that are colored to be invisible, so Prism will include your entire graph with horizontal bar labels.