Steps to repeat:

1. Turn on grid-snapping, at a scale of 16 points.
2. Select the tool "Circular arcs (by center, right and left point)".
3. Draw a perfect half-circle.
4. Switch to the tool "Stretch objects".
5. Deform the circular arc into a straight line, and release the mouse button.
6. Click again on the object and attempt to deform it further. This causes an instant crash of Ipe.

At the command prompt, I see the following output:

Assertion failed on line #504 (ipegeo.cpp): 't != 0'
Aborted (core dumped)

I saved a .ipe file just after step 5 above, and I'm attaching it to this bug report. (I saved it with a .txt extension, just so that Github wouldn't reject it.) If you attempt to open this .ipe file, it causes Ipe to crash immediately in the same way.

[crash.txt] (https://github.com/otfried/ipe/files/12280506/crash.txt)