[pluma]

I'm assuming you're a native German speaker too? Must be a regional accent thing, then.

The closest I can get to ambiguity by slurring "neunhundertsechzig" is "neun oder sechzig" or "neun, neununsechzig", never "neunundsechzig", and I have to make an effort to speak faster than I normally would even if I was reading out numbers in a hurry. I've also never run into this ("hundert" and "und" being mixed up) in my daily life, so I'm surprised to hear that this is something you hear often.