I have a M4 and four magazines (a full 30 bullets, a full 20 bullets, an empty 20 bullets and an empty 10 bullets one). I have the fully loaded 30 bullets one attached to my M4 but whenever I press the F key the game shows extra options for me to reload my M4 and switch magazines.
The expected behavior is not seeing any reloading option when you have a full magazine inserted in your weapon, so if you want to switch magazines you will have to do it manually by using the inventory screen or then shoot once before the game shows your the message to reload.
When you are opening doors or drinking from ponds/wells you will often press the F key multiple times and cause your char to make unwanted reloads, which prevents you from shooting.
A video would be better, but I have a few screenshots that may help understanding the problem: