Ya, happened to me too.  If a cannon shoots even 1 second before you capture a planet, the "bullet" still keeps heading toward that planet.  It often gets there (cause they travel so slowly) after you have captured it; even after you'll left the well.

I agree, Novalith cannons should be build in pairs and ffs dont put them on autocast. Manually target 1 enemy planet with 2 novalith or 1 novalith for an asteroid (if I remember correctly, Novalith Cannons do 3500 points of damage).

ok... so to every1 taht will say i'm too lazy.... you are Right i AM!!!

here is what i do when i play TEC on a MULTI huge Random ....

first of all.... the Novaliths on ur 1st System will shoot at ANYTHING that is unfriendly.... even outside the system itself...

so when the shot is fired.... it can take a LOT of time( I timed one that took 13 minutes to hit his target )      b4 hitting the planet.... so what i do is....LOL.... omg ppl will laugh at me... but hey ... it works...

i leave the cannons on Auto cast... and when i capture a New planet, i build the Planetary sheild AND i upgrade the planet health at LEASST 2 times.... b4 doing ANYTHING else..... so if a shot comes by and the planet is already mine.... well... it WILL survive the shot!!!

that's how lazy i am Folks

No it is fine the way it is.