Weird Highlighting Splodges

When I highlight sentences in a pdf document it doesn’t highlight as you would think and makes weird yellow splodges in the vague vicinity of the text ??

Is this a bug or deliberate program behaviour? I have enclosed a screenshot
Screen shot 2011-01-04 at 08.04.38.png

It’s of course not supposed to look that way. Which version/edition of DEVONthink and Mac OS X do you use? Could you send a document before/after highlighting to cgrunenberg - at - devon-technologies.com? Thanks in advance!