Richard, this is not completely harmless. The ANS for get has this
paragraph:
get finds a property on the property list2 of symbol whose property
indicator is identical to indicator, and returns its corresponding
property value. If there are multiple properties1 with that property
indicator, get uses the first such property. If there is no property
with that property indicator, default is returned.
Similarly, remprop removes only the first matching property. All this
makes it possible (in a non-multi-threaded application) to make a
temporary change to a property and get the old value (if any) back.
This may have been acceptable technique way back when, but certainly
ugly today. I hope no Maxima code is doing anything like this, but way
back when was when much of Maxima was written...