Shredded grass - problem mower?

Hi me again with more lawn problems!

After mowing the tips of our lawn look shredded and they go brown. I assumed this was a problem with our mower (Brand New Qualcast Rotary Mower). Having read the instructions we have adjusted the blades to exacly what is say's but it is still doing it. As per previous post this is a new lawn, turfed with a type of meadow grass which currently has lots of seedheads. Could it be the seedheads which are not cutting cleanly and leading to the brown bits? Any thoughts would be much apreciated.

Thanks again EGW xx