Do T-Addresses stay active?

Hi There,

Today I made my first transaction from my T-Address to Poloniex.
Now something strange happened (which is probably normal behavior) that I wanted to check.

zcash-cli getaccountaddres "" now returns a different T-Address.
What does this mean for the T address I used before? I am mining towards my T-Address so I hope it stays active, do I have to change my mining address every time I do a transaction? Or does the system just activates more and more T-Addresses as you keep on using the network.

Thanks in forward.