While programming an applet for polynomial functions and comparing factors and multiplicites I stumbled over a strange behaviour of the Factors command in Geogebra classic 5. It can simply be reproduced:
Type the following commands:
f(x)=x^2-1
a=Factors(f)
Result is correct: a is shown as { {x-1,1}, {x+1,1} }
Now change f(x) to f(x)=0 by typing f(x)=0.
Result is confusing: a is now shown as { {x-1,1}, {x+1,1}, {0,1} }
Type f(x)=0 again:
Result is growing: a is now shown as { {x-1,1}, {x+1,1}, {0,1}, {0,1} }
The factors list can be resetted by using any other definition of f(x) unequal to zero. That's my suggestion for a work-around.
A little confusing is the result for f(x) = 1:
The factors list is shown as {{0,0}} which of course is unique and can be interpreted as 1, but I have a doubt that it's intuitive for pupils.
The same problem 
Thanks, we'll check!
Fixed for next release (v504)
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