a href tag Is Rewritten By WordPress

I wrote a plugin that implements a catalog. For catalog entries, I post the contents of several fields to wp-admin/admin.php?page=my-thingie (not actually called that)

One of the fields is a text field implemented as an editor by CKEdit. It has a link implementer which creates copy like this:

<a href="https://www.ottodix.org/catalog-item/123.001/">text</a>

I added some debugging code to see the contents of the $_REQUEST in admin.php. If I reference the $_REQUEST item at the beginning of the file, it looks like this:

<a href="https://www.ottodix.org/catalog-item/123.001/">text</a>

i.e., exactly as it existed in the form. However, I reference it at the beginning of my plug in, it looks like this:

<a href="https://www.ottodix.org/%22https://www.ottodix.org/catalog-item/123.001//%22">text</a>

Why is wordpress doing that and how do I make it stop? (Or what do I have to do to so it won’t rewrite that?)