Here are some other threads with examples of this:

http://www.flyertalk.com/forum/briti...ding-pass.html

http://www.flyertalk.com/forum/briti...amsterdam.html

http://www.flyertalk.com/forum/briti...s-checked.html

http://www.flyertalk.com/forum/briti...n-bio-lhr.html

I'm still trying to work out what triggers this, I haven't personally had it, but the first reports of it date from February this year. In any event the issue of boarding passes at the airport takes no longer than usual, the ground staff don't see anything particularly odd about the booking at their end, and so allowing an extra 5 minutes to get boarding passes at the airport should be sufficient.