Does this have some special meaning?
No. I've never encountered a dakuten with a special meaning.
... or is it just some sort of printing error?
A printing error in this case is unlikely. I think that it has to do with the font that they are using. Just as with English fonts, some characters change slightly, like with the lowercase 'a' in English. For example, the font on my computer puts the dakuten underneath the line on your question. (shown below)
Then, I changed the font, and I got a different result:
The moral of the story is you're noticing different font styles! For further information on why the font styles differ, look at the other answer.