Houdini 15
Create a box
Createa a PolyExtrude node

Select a face on the Z-Axis of the box for the PolyExtrude node as group
Set divisions to something higher than 1
Set Spine Shape to Curved
Enable Transform Extruded Front
Set Transform Space to Global

Now when you extrude it all looks correctly

But when instead of extruding on the Z-Axis, you extrude a face on the Y-Axis or X-Axis, it looks like this

Can you post a hip file? I'm following your steps, but I'm not seeing the same results you're getting…

Well yeah, it gives that result, but change the trans. space to local then.
Not saying it's expected to give this result when set to global, I have no idea TBH

I had that too, but somehow it magically worked suddenly when T started tweaking the curve. I still can't make the extrude fit the curve, which is essential when using extrude along curve.