The phrasing of your question isn't exactly clear as to the problem that you are experiencing but let's take a stab anyway...
Casework, as I believe that you may be aware, has Depth, Height, and Width included as Built-in parameters.
Furniture has none of those.
When the family was casework it probably used those D/H/W Parameters associated with something in the family. These exist in the casework template (as labeled dimension controls to reference planes).

When you change family categories any of the built-in parameters become family parameters in the family (assuming that the new category doesn't also use built-in parameters of the same name) and can be edited, renamed, removed, etc. if they have a value in them or are otherwise in use in the family as a labeled dimension control, if not they are simply deleted from the family.
My guess is that the height value is being used in the family somewhere, got converted when you changed categories, and is therefore being reported to you.
That's about as far as I can go without more information or the family file to look at.
-G
Gary J. Orr
GaryOrrMBI (MBI Companies 2014-Current)
aka (past user names):
Gary_J_Orr (GOMO Stuff 2008-2014);
OrrG (Forum Studio 2005-2008);
Gary J. Orr (LHB Inc 2002-2005);
Orr, Gary J. (Gossen Livingston 1997-2002)