Trim error - (Bug?)

Designing a silly chair in grasshopper and running into a problem:

I'm drawing a bunch of ellipses, and then trying to trim them using a brep(a box) but for some reason, some of them aren't differenced. All was working before I updated to grasshopper .8003 so hoping this helps uncover a bug.

attached ghx file has an example of where the error is happening dragged up to the upper-left corner of the grasshopper layout... any help would be appreciated.

For now I've cheated and baked the ellipses + box into rhino, split the curves, then referenced them back into grasshopper using a crv parameter but would be nice to have this fixed.

Cheers,

Alexander