3.4.5: Some Creature Token Art Locked?

I'm not sure if this is a bug or simply the result of some toggle I've overlooked somewhere, but since updating to 3.4.5, my players noticed that certain creature tokens weren't displaying--showing just a generic "padlock" icon rather than their art. Why some creatures were displaying art and others weren't was initially quite mystifying, but I soon sorted out that those that do display their art are all PNG files (utilizing transparency), while those that don't are all JPGs (which of course aren't transparent).

Oddly, all of these tokens (the PNGs and the JPGs) appear normally (showing art) in my GM client; it's only player clients who can't see them. This discrepancy turns up even when I run GM and player clients side-by-side on the same computer; I can see art as a GM, but not as a player.

So, anyway, I'm in a muddle. Have I somehow accidentally "locked" player access to JPG tokens?

 

P.S.: I just checked and the same issue affects item tokens as well. It does not affect maps, however; I use JPGs for those and they're fine.

 

That did it! Thanks a bunch!