Putting 2^49 into Alfred yields 562,949,953,421,312 - as expected.
Putting 2^50 into Alfred yields 1,125,899,906,842,620 (copied-to-clipboard value is 1.12589991e15).
Hence, the display is incorrect with thousands separator (Features->Calculator) enabled. The underlying value is in scientific notation, but the displayed value is simply given trailing zeros to compensate.
Thanks for looking!