This is still happening 3 years on. Has there been any response to this yet?
I found a solution for my particular instance. If the annotation with leaders is grouped in the table of contents with imagery or other layers that have special symbology (eg hatching or transparency) the leaders rasterize when pdf'd. Change the grouping and the text should come out clear and complete.
I found the same behavoir and solution! I can even reproduce the error, if I put the annotation back in the group.