Comment 8 for bug 1780363

The issue those lines are trying to fix is one of comprehension.

Double click a symbol to have it placed into the edit canvas.

Now single-click on a different symbol. The highlighting of the just-selected symbol is more visually noticeable than the highlighting for the currently-on-canvas symbol, making it very easy to think that you're editing a different symbol than you actually are.

The scrollbars jumps on OSX to make sure that the symbol-on-canvas highlighting is visible when you're editing the symbol.

The video in #7 certainly appears to show that something different happens on Linux.