To me it shows a complete lack of respect for your work, your clients and your colleagues.
Someone spotting (or tracking down a shipment of, in your case
@TPoseOnTantrum) track essentially 'in public' and posting something is entirely fair game, in my opinion. That's not really leaking something, the onus there is on the shipper (for example) to appropriately label their stuff. That's completely different to snapping a photo of some confidential plans in your office and then posting them online.
@Lofty is right - I am covered generically by my employer's NDA agreements with our clients (in general, the details of all of my work is essentially under an NDA unless I have specific permission to share it), and this is commonplace in the UK (and I would assume a lot of the rest of the world too).
