Spark notes output is sometimes unreadable

Hello,

First, thanks for developing Zeppelin, it really is a great tool.
We nevertheless have a small but annoying problem occurring in some notes;

Some of our users are reporting "white on white" output when running a note, as seen in the screenshots below:

The users are using the Spark interpreter, if that is of any importance.
Do you have an idea why this could occur ?

Thank you.