When a coin stakes, it splits the coin stack in half and adds the staked amount to both. So, when you have 100 coins and it stakes, you will have two stacks inside that wallet address with a value of 50+the stake. Meaning; when a coin stakes, it creates two stacks of itself that then go on to stake separately. What you see is the difference between your settled "confirmed" and unsettled funds "unconfirmed" (newly staked) coins. Both stacks go on to be confirmed at the same rate, but when one of those stacks then stakes, it will take your total down pending confirmation. It seems a little complicated but it's how it works with every stake coin. Every coin inside your wallet goes towards your weight, but more confirmations typically increases weight.