How to keep pointed stroke on a triangle after expanding?

Question

How do I keep my pointed bottom edges of the triangle sharp? I have a triangle with a stroke but after I expand the shape it looses it's pointed edges but only at the bottom, why is this? I haven't had this problem with any other shape besides a triangle.

Screen shot of before (left) and after expansion (right):

Answer 1

Your example doesn't look like it's been expanded though...

Here is a triangle (drawn using the Polygon Tool) with a white fill and a black stroke:

Note: There is one closed path.

Here is that same triangle expanded (Object > Expand):

Now there is a group with a white polygon and a compound path where the stroke had been...

And here is the first polygon with the bottom section separated from the main triangle:

Looks a lot like your example...

Here's what's going on (I think):

If I'm correct, and you have two paths, just select them both and press Ctrl+J to join them together: