To quote Bees!, who was quoting me:
'"It is just me or does the Fox Brush take 2 units of wear every time I brush a fox?" - this is a bug, oops'
as said here.
Just thought I should say that it is still taking 2 units of wear with every brush, however it is a rather minor thing but I just thought I might as well mention it before I forget about it and for all I know it is intentional now.
Also on a slightly related note, but not really because it is not a bug, is the Hoe Down upgrade card really suppose to make it so the hoe uses 5 units of wear every time it is used?