Early in my vintage bike hobby I picked up a Peugeot Carbolite 103 mixte for my wife that, after I brought it home, I noticed had exactly the same bulge. Not being terribly smart about these things I didn't think much of it. The frame and fork were otherwise straight. I spent a day swapping out components to make the bike lighter, re-wrapping the handlebars, with the intention of giving her a really dolled-up bike. When I was done I took a test ride in our driveway not realizing I hadn't tightened down the handlebar clamp sufficiently. As I tried to brake, the handlebars slipped and I ran into a chain link fence at maybe five mph. The frame bent nearly in double at the bulge, leaving the fork and front wheel untouched.

I don't doubt that Ishiwata 022 is stronger than Peugeot Carbolite, but I wouldn't trust it.