Problem with integral on WP 34s

[lrdheat]

Unrelated, but interesting…integral of x*e^-x from 0 to infinity should be 1. When integrating from, say 0 to 1,000, it converges on 1. If I integrate from 0 to 1,000,000, it converges on 0, misses the important part of the curve close to 0. How, then, does the WP 34S on DM 42 recognize the important part of the curve when integrating from 0 to infinity (it converges on 1!)?