Preview package cutting off top of content

Question

When the preview package is loaded, the tikzpicture/figure environment that I am trying to isolate becomes set too high, resulting in the top of the image being cut off. (This is similar behavior to the "Side Question" part of Code to ignore all of document except for list environments and sections, so I don't believe it to be directly related to the tikzpicture or figure environments, nor the floats option.)

However, when I load the preview package with the tightpage option, everything comes out fine (so long as I have made the papersize big enough using geometry beforehand, as has been mentioned in this answer). I'd like to be able to have all figures on a common page size, however, so tightpage isn't really what I'm after in this case.

What causes preview to incorrectly place the content and effectively trim off the top?

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preview version 11.87, dated 2010/02/14

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MWE:

\documentclass[]{article}

\usepackage[a3paper,landscape]{geometry} % Make paper super big, fixes tightpage option cutting off right of image

% This works okay now with tightpage option set once papersize is made bigger
%\usepackage[active,floats,delayed,tightpage,pdftex]{preview} 

% Without tightpage, this form still cuts off the *top* of the image
\usepackage[active,floats,delayed,pdftex]{preview} 

% Define a few styles for use in making the figures
\usepackage{tikz}
\usetikzlibrary{shadows,arrows,positioning}

\tikzstyle{block}=[
    draw, fill=blue!80!black!20,
    anchor=north,
    text width=13.0em, text centered,
    minimum height=1.5em,drop shadow]
\tikzstyle{flowline}=[
    draw, very thick,
    color=black, -latex,
    font=\tt]

\begin{document}
\begin{figure}
\centering
\begin{tikzpicture}[]
% Nodes
\path             node  (p1)    [block] {Flowchart Block Text};
\path (p1.south)+(0,-1.5) node  (p2)    [block] {Flowchart Block Text};
\path (p2.south)+(0,-1.5) node  (p3)    [block] {Flowchart Block Text};
\path (p3.south)+(0,-1.5) node  (p4)    [block] {Flowchart Block Text};

% Connectors
\path   [flowline]  (p1.south) -- node [right,align=left] {Flow Label} (p2);
\path   [flowline]  (p2.south) -- node [right] {Flow Label} (p3);
\path   [flowline]  (p3.south) -- node [right] {Flow Label} (p4);

% Alternate Start
\node (p1alt) [block,left=of p1,text width=10em] {Flowchart Block Text};
\path   [flowline, dashed]  (p1alt.south) |- node {} (p2.west);

% Optional Output
\node (next) [block,right=of p4,text width=10em] {Flowchart Block Text};
\path   [flowline, dashed]  (p4.east) -- node {} (next.west);
\end{tikzpicture}%
\label{workflow}%
\end{figure}%
\end{document}

Answer 1

I don't know why this happens, but the option baseline=0 to tikzpicture seems to do the trick:

Without baseline=0 option:

With baseline=0 option: