It appears to be a result of how the shape was created. I believe you used the star tool and then set the points to 3. I am not sure why this causes a problem but it was relatively easy to fix.
The first thing I tried was tip number 2.1 here Inkscape Tips and Tricks
That did not solve it but I do believe it was needed as you had moved the triangle after putting them in their groups.
The second thing I did was tip number 8 (which i just added) here Inkscape Tips and Tricks and that fixed it.
Here is the one I fixed if you want to compare it.