Hi David,
For now, you may use the following as a solution.
Add the following code segment to your CSS files or positioning.css file provided in default webhelp. This basically hides the abstract section since it has the css class name 'abstract'.

.abstract {
display: none;

I'm not sure adding this to the default webhelp output though. Since the abstract is coming from docbook xhtml stylesheets, some users may be using it. This is not particularly a bug. From the description, I take it you don't use generally add abstract section to the source?