The symbol in question is a standard architectural detail label that has a circle outline and contains text.
It came from our client pre-converted to pdf, and I don't know the native cad app that produced it.
These symbols appear as-desired when viewed on screen and on the print preview; yet on the hardcopy, they turn into solid black areas the same size & shape as the circle; obscuring the text. This issue occurs inconsistently, and appears on diverse printers. I've tried swapping printer drivers, changing the color settings to grayscale black-only and high-quality, and have experimented with other user-selected variables. The symbol has no visible shading.
How does one prevent this from happening?