Vim in terminal assumes default terminal size

It looks like vim is assuming a default terminal size of 24 columns and 80 rows. This means

1. If the terminal panel is smaller than 24 rows high, the bottom is cut off and artifacts appear when scrolling
2. If the terminal panel is larger than 24 rows high, vim doesn't use all available space.

In general, the full width of the terminal panel is not used either.