This isn't a bug, it's just how that particular event is coded.
I mean, everything in the game happens because that's how it was coded, including bugs.
I was more reporting the fact that it makes no sense using in-world logic, which is the defining characteristic of a lot of bugs. (It's also somewhat frustrating to figure out how that particular event works : Why would you assume it to be based on your own vision rather than the Sentry's?)
Disable at your own risk!
I'm not sure how i'd be disabling my Visual Processing Units with any risk, given that i usually know if there are other hostiles nearby, and that almost every time, i'll prefer missing a few shot against the sentry from not seeing it¹ rather than having tracking reinforcements sent after me.
(¹With traps or a good Sensor Array, i wouldn't even need to shoot in the dark.)