Weird lines inside UI scroll frames

[ahbnr]

(reported by @didge-rydu )

Many of the UI screens use a scroll background. In these scrolls panels with decorative frames are often used. When running the game, oftentimes vertical lines in the same color as the frames appear within these panels.

Steps to reproduce
One possibility to observe this issue:

1. Start a new game
2. Connect a player
3. Observe lines within decorative frames of the lobby screen