I don't want to give it away but I received the reward for "The Glaviz Incident" and it was installed on my ship.
Now my ship is 313/308.
How can I have more items installed taking up more space than I actually have?
is this a bug or a known issue?

Same thing happened for me, so i just uninstalled a few things to make the space, i think that since its automated, it ignores limits when installing

It is not a bug. It automatically installs itself, sometimes over the limit. Note that you CANNOT install anything else when your ship is over encumbered. Most mission module rewards automatically installs themselves.

just wondering, what is the stats for the Zolazin Jammer?

Zophah,
earn it and you will answer your own question.
It is well worth the trouble when you closely examine it.
At first I mistakenly thought 'oh great this isn't worthwhile' however when I divided what the jammer does vs. space it's very efficient.

It's very nice and efficient. I will end up with two no problem. Again, if your new try and complete these special missions at least once! Well worth it.