When creating documents to validate with the XHTML doctype, the ampersand character in any URL needs to be escaped as an HTML entity & ...TextMate will perform this automatic transformation on copied items when you select text and use the "Wrap Selection as Link" command. It takes the clipboard contents, filters it, and uses the result as the default URL in the link. However, if the URL from the clipboard already has escaped ampersands, TextMate will transform the entity as &
Clipboard Example: /some.php?option1=foo&option2=bar
When the Wrap Selection as Link command is issued wtih this URL stored in memory, you get something like the following:
<a href="/some.php?option1=foo&amp;option2=bar" target="_blank">some link</a>
TextMate's default behavior may need to be adjusted so it checks for escaped ampersands in a URL before attempting to transform it.