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You enter the "taxable" amount (1040 line 16b, not line 16a) in Worksheet B line 9 columns A and D. It's not taxed by Maine, but it's used to compute your Maine tax. Almost all states with a state income tax calculate the state tax on your world-wide income (adjusted for state law), and charge you the proportion of that tax due to income associated with the state. Your pension income increases the world-wide income and the tax so calculated, but reduces the proportion, leading to a small increase in actual tax paid.
Thank you. I am certainly not happy about paying taxes on a pension totally separate from maine wages and the small increase noted about is over $1000 which I owe Maine now. I moved out of Maine because of all the taxes they burden residents with, and I still can't get away from them. Sorry for blowing off steam and it isn't directed at you! Thanks again.