If you are speaking of yourself as the agent, it would never be appropriate to use the third person ("fixes a bug"). If you are speaking of your work, it is not wrong to use the present tense to describe what it accomplishes.
A simple Google search for "this release fixes a bug" returns close to three million results in which the present tense is used to describe an activity that has already occurred. (N.B. The corresponding search for "this release fixed a bug" turns up a mere 800,000 entries.)
Remember that the present tense is also used to describe an ongoing condition or continuing state (see How do the English tenses correspond temporally to each other).
Using the present tense is appropriate here, and, curiously, using the past tense would possibly cast doubt on the accomplishment (which may be why the Google search for the past-tense construction turns up so relatively few hits). If I say "this release fixed a bug" it might imply that the fix was no longer successful, and something came along which counteracted it.