Webpage test user agent string missed to handle one of user agent string

Hi team.
we see webpagetest is not passing User agent string correctly for one of my page
https://www.ancestry.com/cs/offers/freetrial

for this page deksktop and mobile view is different .
mobile view is correct when actually renderred by real mobile device or chrome lighthouse audit .

but when simulated using wpt test , its using different user agent string.

I understand that by passing custom user agent string we can make this work (which is actually working ), but i think instead of bypassing what actual user using User agent just to get our desired results will not be right approach.

so please consider this as an defect

wrong view :
https://www.webpagetest.org/result/200309_3K_286874b830ba0e28431dd17e57ff46b1/

(user agent : Mozilla/5.0 (Linux; Android 4.4.4; Nexus 7 Build/KTU84P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.146 Mobile Safari/537.36 PTST/200226.180231)

correct view :

https://www.webpagetest.org/result/200309_13_abd42583f9a5bd614dafe5e704caa75a/

(user agent : Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3694.0 Mobile Safari/537.36 Chrome-Lighthouse PTST/200226.18023)