Plugin: Adding Top-level menu inside folder errors

Hello,

I was experimenting around with adding administration menus via plugins and found this strange error. I took the sample ‘Menu Test’ plugin on this page:
https://codex.www.ads-software.com/Adding_Administration_Menus
and placed it in two locations:
1. in wp-content/plugins/
2. in wp-content/plugins/menutest/

In #1, clicking ‘Test Toplevel’ works perfectly.
In #2, clicking ‘Test Toplevel’ gives the following error:

Fatal error: Cannot redeclare mt_add_pages() (previously declared in C:\Development\wordpress\wp-content\plugins\menutest\menutest.php:13) in C:\Development\wordpress\wp-content\plugins\menutest\menutest.php on line 11

Somehow a function redeclaration check isn’t being applied when the base plugin file is placed in a subdirectory of plugins/. This seems to only be a problem when the plugin uses add_menu_page (since Spam Karma 2 is housed in a subdirectory and has no problems with the menus).

Anyone have any ideas?

[edit]I’m using version 1.5.2[/edit]