File this one under “Why Are We Not Surprised?”: City investigators have found irregularities at a nonprofit tied to Brooklyn political boss Vito Lopez.

Troubling? Yes. Shocking? Hardly (alas).

Lopez has long been under scrutiny, particularly after a series of reports in The Post.

He’s a master at Nonprofit Polka — the dance that lets lawmakers amass political power and riches. Legally or otherwise.

According to a new city Department of Investigation report, top execs at the Ridgewood Bushwick Senior Citizens Center — which Lopez founded and which gets millions in public funds — tried to show that their sky-high pay was perfectly legit by using wholly fabricated documents.

DOI says Christiana Fisher, Ridgewood director (and Lopez’s campaign treasurer), admitted she “recreated” the records; the originals, you see, had been “misplaced.”

No doubt she and Ridgewood’s housing director, Angela Battaglia (also Lopez’s girlfriend), were in a fix: Probers wanted to know how they got their huge salary bumps in 2009. (Battaglia’s pay shot up from $198,000 to $343,000; Fisher’s went from $336,000 to a whopping $782,000.)

DOI also says the group filed tax and expense reports with numerous inaccuracies and wrote “counterfeit” checks, plus other violations.

But while the probes continue, City Hall is sticking by $69 million in contracts with Ridgewood.

“Corrective action needs to be taken,” says a mayoral aide, but “the new board members know that.”

Comforted? Neither are we.

All this hanky-panky is made possible by a system that lets pols — city and state — channel money (pork) to groups of their choosing.

Alas, until those systems are gone, don’t expect much to change.