Survey Resource 3 (Source)

Hallo,

ive a question about survey xp...im sitting on a 90% spot of chem with artisan xxx3...While sampling for ressources it happend sometimes that i get 39xp for a 9unit sample...so far so good...but for a sample of 10units i obtain only 21xp... is this a "bug"? im grinding now for 2 days on survey and saw this more than 10 times.