Hi and welcome to SPT.
This is not a bug. This is normal behavior.
Rounds in the chamber are not counted in the magazine count. When you spawn in a raid, the first thing your character does is racking the bolt, which puts 1 round from your magazine into the weapon chamber (so you can shoot).
The SKS in your screenshot have internal magazines. When you reload your SKS, your character racks back the bolt, which ejects the round that was still in the chamber. Then your character tops off the magazine with the bolt locked open. As soon as the reload is finished, your character releases the bolt, which again puts 1 round from the magazine into the chamber ( so you again have 9 rounds in the mag, 1 in the chamber).
Before a raid you can inspect your weapon and manually put a round in the chamber and have 10 shots in the mag (so actually 11 rounds, 10 + 1), but simple reloads will still just give you 9 + 1.
I hope this helps.
Have fun 
