When I search for text, the regular expression setting does not persist.  There
are two ways in which I notice this:

1) I enter a regular expression, check the Regular Expressions checkbox, press
the Find button and it finds a match.  If I now press the Close button and use
the navigation arrows at the bottom right of the screen, below the scrollbar, I
can navigate from one match to the next and back.  However, if instead of
pressing the Close button in the Find dialog, I close the Find dialog with the
window manager's X in the window's titlebar, the text in the Search For input is
treated as a literal string, not a regular expression.

As an example: I type "while|since" into the dialog, press Find, and it finds an
occurrence of "while" in the document.  Now I press the window manager's X to
close the dialog.  I press the double-arrow navigation button at the bottom
right, below the scrollbar.  It now fails to find any matches in the entire
document, because it is looking for a literal "while|since" which doesn't exist
in the document.

2) The other place I notice this, and this might not be the same bug, is that
when I have previously searched for a regular expression and re-open the Find
dialog, the Regular Expression setting is no longer selected.  I have to
re-select Regular Expression each time I perform a new search.