It occurs along the entire first half, from the toe to the middle.
Upon inspection, I can see fine lines, parallel to the edge, running through the bevel. I looks as if the ruptures occur at these microcracks.
I have raised the honing angle to 6 layers of tape, without any improvement. I also expected to get rid of the problem, once I got into "fresher" steel. Not.
The blade didn't taper near the end. Actually it is a bit wider near the toe, as typical on many of these old blades. By the way, the razor is a wedge (slightly hollow). I don't have an overly wide bevel, which seems to suggest that the honing angle is not too shallow.

Bart.