When I enter the game I occasionally will have a fraction of ammo in my reserves than what I should have. I play with the default Engineer gun sometimes and will enter the game with 123 or so instead of my 150. I know people who have seen this too. Intentional? Or bug?
From what I know when you log into the game you've got the amount of ammo you had when you left the game. So if you leave the game with an empty gun you'll come back into the game with an empty gun, luckily you'll spawn in the local warpgate so a resupply computer is always nearby. But yeah, I honestly do not see any reason at all why this is case. A change to give an automatic resupply upon logging in seems no more than logical.