Help. Is this normal for the DA 18-135?

I just acquired a used DA 18-135 and noticed right away that after zooming it is necessary to refocus. If so, this is not a true "zoom" lens, but a "vary-focal" lens. I have a Katz-eye split image focusing screen so the focus change is very obvious as I zoom.

Is this within design specs, or should I return it?

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Jonathan Blocher
Instructor of Art, Design, and Humanities
mrblocher.com