this is the 3% synergy bonus beam cannon that I upgraded to Mach IV using 220 artifacts. The unique bonus still applied to the purple beam cannon, as its icon was the same as the previous version at Mach III (when purchased). Once I upgraded the weapon from Mach IV to Mach V it removed the unique icon and replaced it with the standard beam cannon icon. This either means that the weapon upgrade removes the bonus or that the bonus, when upgraded to mach v, needs the icon replaced to reflect that this is, indeed, a mach v beam cannon that gives 3% synergy.
Sadly i have no pictures of the weapon before it was upgraded, however the alien camo on the styx shows clear as day.
This bug is known and should be fixed soon.
Potentially bad news. I found a similar thread over on the Russian forums, and this is what was said:
Mk5 currently not inherit bonus. Technically it’s not a bug, but is likely to inherit will be done.
inheritance will be made for subsequent purchases or will be added as well for those who have already made the Mk5?
It is not clear
So there you have it. The developers haven’t decided if they are going to make the update retroactive or not. Which could be very bad for those of us who didn’t realize that Mk 5 was ‘bugged’.