Yeah most prob you miss typed something caps lock or if you have other languages on your keyboard this can also be the problem as some special caracters are on different place in this situation. I don't believe that it is an client bug tho.
Maybe due to some copying from folder to folder the wallet.dat file got damaged? Still the ballance is right and even some incomes happened from mining. I have the same password on two wallets. One is working, one says incorrect, so I doubt I misspell it somehow. I agree it's very strange, but last time I had same problem it suddenly worked. The password haven't changed.
