Something rewrites my php

Hi, I hope someone can help i’m sure i’m doing something stupid but i’m just a beginer so please have patience.

Something is rewriting my php code!

I write the following code into a nav.php file which gets called by header.php to give myself selected main navigation options at the top of the page

<ul>
<h2>
<li><a>/">Home</a><?php wp_list_pages('include=29,94,2,4,41,129,126,131,133,37&title_li='); ?></li>
</h2>
</ul>

When i upload this to the theme folder it works and only displays the page links i want. but if i want to add another included page, when i download nav.php to alter it something has changed the code to

<ul>
<h2>
<li><a>/">Home</a><?php wp_list_pages(

Is this because i have made a mistake in my code and if it is can anyone please spot the error and let me know.

thanks

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