As Steve said you are most likely going into neutral as during that gear change you go out of first then into second and has perhaps a longer throw than other gear changes and needs a deliberate change rather than a flick of the toe
On my bike there is usually a clunk when second is fully selected
Check your linkage for TOO much play and adjust it accordingly, the stock heim joints are poor at best Stainless Heim Joint - Bungking.com / Big Designs
Look here, I used these with good results:s