A Flaw??? Or not a Flaw??

Hmmm, I hate to say this but I think that I might have found a flaw in the new Harry Potter book *gasp* I know but I re-read that section over again and I believe it is one. It was somewhere around chapter 23 when Ron, Harry and Hermione are all talking about the "Hallows". They are all saying Voldemorts name several times, I am there thinking why are you saying that name it will send the death eaters?? Then I thought ok, well I will read on to see if they show up in the next couple of lines...but no death eaters...so I read on to the next couple of chapters, when Harry finally says it again and sure enough some "Snatchers" appear. But I am still confused as to why nothing happened the first time or for that matter why the death eaters didn't come out the second time...and instead of the death eaters we got the "Snatchers"??
Lol, I guess I will read on and perhaps it will answer my own question...