eTrex Touch 35 distance incorrect

Hello,

My total distance is only 30km, but when i look in detail, i can see that i walked 42km???

My watch is also saying 42km...

 

How come i see 30km walked? On the handlet i also saw 30km... 

I doubt that i walked 12km slower than 1.5km/h

Thanks for reading and helping finding a solution