is there any limit for encode time matching decode

[rangercyh]

I have found everytime I want to encode something I must create a aes.ModeOfOperation, such as

let aesCbc = new aes.ModeOfOperation.cbc(u_key, u_iv)
let a = aesCbc.encrypt(xxx)
let aesCbc2 = new aes.ModeOfOperation.cbc(u_key, u_iv)
aesCbc2 .decrypt(a)

when I try this some decrypt failed?

let aesCbc = new aes.ModeOfOperation.cbc(u_key, u_iv)
let a = aesCbc.encrypt(xxx)
// let aesCbc2 = new aes.ModeOfOperation.cbc(u_key, u_iv)
aesCbc .decrypt(a)

or when I try this, some decrypt failed strange too.

let aesCbc_en = new aes.ModeOfOperation.cbc(u_key, u_iv)
let aesCbc_de = new aes.ModeOfOperation.cbc(u_key, u_iv)

let a = aesCbc_en.encrypt(xxx)
let a2 = aesCbc_en.encrypt(xxx)
let a3 = aesCbc_en.encrypt(xxx)

aesCbc_de.decrypt(a)
aesCbc_de.decrypt(a3)
aesCbc_de.decrypt(a2)

Is I missing something?