It is possible to cause GnuCash to crash when exporting a report to HTML. The steps to reproduce are as follows:

1) From an active report, click the Export button
2) In the resulting dialog, click on an existing file in the folder listing.
3) Press the Right arrow key.
4) Click in the Name text box [and add a character to the proposed name].
5) Click the Export button.

This causes the program to crash. 

As a little background, I was hoping to save a new copy of a pre-existing report, so I took steps 1-2. Wanting to rename the report, I pressed the right arrow key. Since step 2 resulted in the file name being placed in the Name text box with highlighting, I expected the Right arrow to move the cursor to the end of the highlighted name and allow me to add new characters to the name. This is, I believe, the standard behavior under the circumstances.

Instead, GnuCash clears out the folder specification and replaces it with a search box. This search box remains in effect when the user clicks on the name box in step four. Meanwhile, the user changes the name and clicks the export button, with the resulting crash.

A couple of points here: 

1) Invoking a search box from the arrow key is not expected--especially when user action clearly highlight the text control (the file name). Input should affect the highlighted control, resulting in the cursor moving.
2) The file location should not be cleared when a folder search is invoked; rather, the previous folder should remain defined until the user actively selects a new destination folder.
3) The Export button should be deactivated if any required data element is not correctly supplied (as in the example of the null folder).