OnePlus 5 user dials 911, the phone reboots (Update: not just OnePlus)
Browsing through the comments shows other people claiming that the same happens when dialing 999 or 112 (the 911 of Europe). However, some claim that they have been able to get a 911 call through successfully in the recent past, so it might just be an isolated issue.
OnePlus has issued an official statement on the matter, which reads:
We have contacted the customer and are currently looking into the issue. We ask anyone experiencing a similar situation to contact us at support@oneplus.net
While knowing that you can connect to 911 when needed is certainly a must, we would advise against randomly going off and dialing the emergency hotline. If you insist on checking if your phone is fine, see if you can call your police department's non-emergency phone, explain the issue, and ask when it would be a good time for them for a test call. Either that or wait for OnePlus to post an update on the matter, or ask support if it's fixed after some time.
Update: Since this has become a hotly discussed issue on Reddit, a bunch of users have chimed in, claiming that it's also a problem for many Asus ZenFone units and possibly other Android devices. The issue seems to stem from custom manufacturer dialers not "talking" well with Android's native phone framework.
source: Reddit OnePlus 5 thread | Asus ZenFone thread
Looks like I should fix this soon
Posted by Nick Morrelli on Monday, July 17, 2017
source: Reddit OnePlus 5 thread | Asus ZenFone thread
Things that are NOT allowed: