Question: Strange change of characters

If I let Maple be running on the computer for a while, maybe a day or 2 or so, I almost certainly get a change of several

characters. See my favourite palette:

 

 

As you can see the eternity sign e.g changes to a big N. If I rerun the worksheet everything works ok except for the change of characters.

Not seen above: :=  changes to d

Remedy?

 

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