PHP Fatal Error with multiple categories on single admin page

(EDIT: It's probably worth checking the next reply first, Drew, before diving too far into this. I was able to fix the error, although I'm not sure what I did to cause it.)

I'm getting a PHP "white screen of death" in the Perch admin on regions that utilize more than one perch:categories set. I can see the interface for all sets just fine, but when I click "Save" I get the blank screen.

So, with a single set, I can save the page as expected, using this code:

<perch:categories id="attributes" label="Attributes" set="attributes">
    <perch:before><p class="label">Song Attributes</p><ul class="listing clearfix"></perch:before>
        <li class="link<perch:if exists="perch_item_first"> alpha</perch:if>"><a href="/filter.html?cat=<perch:category id="catPath" />"><perch:category id="catTitle" /></a></li>
    <perch:after></ul></perch:after>
</perch:categories>

But when saving the page with multiples sets, I get the white screen, such as when using this code:

<perch:categories id="attributes" label="Attributes" set="attributes">
    <perch:before><p class="label">Song Attributes</p><ul class="listing clearfix"></perch:before>
        <li class="link<perch:if exists="perch_item_first"> alpha</perch:if>"><a href="/filter.html?cat=<perch:category id="catPath" />"><perch:category id="catTitle" /></a></li>
    <perch:after></ul></perch:after>
</perch:categories>

<perch:categories id="genres" label="Genres" set="genres">
    <perch:before><p class="label">Song Genres</p><ul class="listing clearfix"></perch:before>
        <li class="link<perch:if exists="perch_item_first"> alpha</perch:if>"><a href="/filter.html?cat=<perch:category id="catPath" />"><perch:category id="catTitle" /></a></li>
    <perch:after></ul></perch:after>
</perch:categories>

The resulting error in the PHP log is as follows (there is an entry for each attempt to "save" the page):

[25-Aug-2014 01:52:08 UTC] PHP Fatal error:  Call to a member function catPath() on a non-object in /path/to/site/admin/core/lib/PerchFieldTypes.class.php on line 1949

The line of code referenced is:

$out[] = array('key'=>'_category', 'value'=>$Cat->catPath());

Working mainly in Chrome 36.0.1985.143, but get the same results using Safari. I've tried removing all other markup in the template except the two perch:categories calls, but the page still whites-out upon saving.

Other observations:

• Upon manually reloading the white-screen page, the data is intact (that is, the choices made both category sets are remembered)
• Restarting the server did not help
• Restarting/clearing the browser(s) did not help
• Using the default set.html and category.html templates

And the diagnostics:

SUMMARY INFORMATION

Perch: 2.6, PHP: 5.4.4, MySQL: 5.5.25, with PDO
Server OS: Darwin, apache2handler
Installed apps: content (2.6), assets (2.6), categories (2.6)
App runtimes: <?php $apps_list = array( 'content', 'categories', );
PERCH_LOGINPATH: /admin
PERCH_PATH: /path/to/site/library.naturalgrowth.ca/admin
PERCH_CORE: /path/to/site/library.naturalgrowth.ca/admin/core
PERCH_RESFILEPATH: /path/to/site/library.naturalgrowth.ca/admin/resources
Image manipulation: GD
PHP limits: Max upload 128M, Max POST 128M, Memory: 512M, Total max file upload: 128M
Resource folder writeable: Yes
HTTP_HOST: library.naturalgrowth.ca
DOCUMENT_ROOT: /path/to/site/library.naturalgrowth.ca
REQUEST_URI: /admin/core/settings/diagnostics/
SCRIPT_NAME: /admin/core/settings/diagnostics/index.php

Let me know if I can supply anything else.