Can't change Block positions or settings: Clicking Save Blocks returns to /search/node

A very odd thing thing has begun happening since yesterday, but it IS a dealbreaker.

I've been customizing a theme (using almost purely CSS) and the process has gone well. But now that I am ready to begin reorganizing my blocks for the new theme, I'm encountering a serious problem.

When I click the "Save Blocks" button on /admin/build/block Drupal sends me to /search/node without an error instead of saving! The same thing happens when I attempt to "Save Block" in the "configure" area for that block.

Does anyone have a clue why this might be happening?

The only thing I can think of that might be of consequence is that I "hardcoded" the search form at the top of the theme (easier than try to make a position for a block). Here's the code for that, if it matters:

  <form id="search-block-form" method="post" action="/search/node">

<div><div class="container-inline"><div class="form-item">

 <input type="text" class="form-text" title="Enter the terms you wish to search for." value="" size="54" id="edit-search-block-form-keys" name="search_block_form_keys" maxlength="128"/>

</div>

<input type="submit" class="form-submit" value="Search" id="edit-submit" name="op"/>

<input type="hidden" value="652cbefab2034310589ece72b0b023df" id="edit-search-block-form-form-token" name="form_token"/>

<input type="hidden" value="search_block_form" id="edit-search-block-form" name="form_id"/>

</div></div> 

And help is greatly appreciated as I am on a fairly tight schedule.

-Garrett