It works correctly for me.

I added $1000 of Unrecaptured Section 1250 Gain to a tax return in the 22% tax bracket, and it added $220 of income tax.

You may want to look at the entire tax return to see if anything else changed besides regular income tax.  For example, the 'extra' income could reduce some credits or deductions or be subject to the Net Investment Income Tax or possibly even AMT.