Small bug, 'invisible' barrels

When alt-tabbing out or switching from the game to something else (say, firefox) and coming back in, barrels and chests will not show up when holding alt until/unless moused-over (defeating the purpose of holding alt to see if there are any barrels/chests hidden in grass elsewhere)

Barrels often show this behavior anyway, even when not going out-of-game. It makes it difficult to find them unless you wildly wave your mouse around.

First noticed on the Terraces, Level 3.

EDIT-
Just in case it helps
PC specs-
XP pro, 4G Ram, AMD Athlon 6400 dual-core, Nvidia 9400GT, running DX9.

CLARIFICATION-- The barrel is there, the chest is there, but when holding alt, the word "barrel" or "chest" does not appear to give a visual indicator that there is something there.