If terminal supports transparent background.....

[c02y]

If terminal supports transparent background, THE area will turn into black block after you hit UP arrow to rotate the piece.

[tylerneylon]

I tried to reproduce this using mac's Terminal, but I didn't see the issue. Perhaps it is os/terminal dependent. I'm using mac os x 10.9.5. What os & terminal were you using when you saw the problem?

Below is how things look for me — no issue.

[c02y]

Fedora 20,

The black block in the previous image happens in Yakuake,
xfce4-terminal supports transparent background too, but if I run the program in it, the transparent background will turn into a piece of black background. like this: