Is this normal?

I'm an IB analyst at a mid-market shop and recently encountered what I would consider questionable or unethical business behavior. Specifically, we secured a sell-side/spin-off mandate for a well-known family-run company undergoing a restructuring. It isn’t yet clear which parts of the company will be sold, and there are other considerations such as the family’s reputation if the entire business is dismantled or sold off in pieces. (all of this is not public and highly confidential) 

The client instructed us to perform a pre-screening or market testing, explicitly telling us not to disclose certain information—such as client names, revenue splits, etc.—when reaching out to potential investors.

However, on a recent call with my MD and some prospective investors, my MD displayed a slide showing the company’s largest clients. He openly stated, “I was told not to show you this, and when we send over the materials later, we won’t include this slide—but if you happen to take a screenshot, that’s just the way it is.”

I found this disturbing, as it seems to violate the client’s instructions and is essentially abusing their trust. I’m wondering if I’m being naive to consider this unethical, and whether this is common in the industry or more specific to my current firm. I’ve encountered other situations like this, so I’m trying to figure out if it’s just “how things are done,” or if it’s genuinely improper.