This is what happens when I mod the client and fire up sit n gos:
There are two rectangular areas that aren't covered by the table/background mod in the upper left and lower right corners. The mod looks fine on my computer when I open cash game tables, the problem only occurs for sure during sngs. I haven't tried an mtt yet.
Edit to add: I should also mention that I only tried the sit n gos using mini view, so I don't know if the problem also occurs in classic view or not. I'm done playing for today but I can verify this tomorrow.