In brief, just don't use XsltListWebPart on Application Pages.

And here are some summarized explanations:

XsltListViewWebPart and other OOTB SharePoint webparts (especially complex ones), apparently just aren't supposed to work in Application Pages environment. In other words, they weren't tested there and thus their operability is not guaranteed.

This can be indirectly confirmed by reading at least the following MSDN articles:

• Creating Application Pages for SharePoint
• SharePoint Page Types

.. A site page can also host features such as dynamic Web Parts, and Web Part Zones. Application pages cannot do these things.

Also it is stated in MS course 10232.

Concerning XsltListViewWebPart (XLV) in particular, I heard of multiple problems while using it from Application Page, and experienced some of them myself.

For example, if you customize XLV using XslLink property, XLV will fail to cache the xsl file, and as a consequence, ECB and corresponding buttons on Ribbon will not work. In logs, you will get the following exception message:

Attempted to use an object that has ceased to exist.

Also, you can check out the following question for another example of problems with OOTB webpart on application page (ListViewWebPart, this time):

• Edit or Add ListItem to List in ApplicationPage with ListFormWebPart or DataFormWebpart, but how?

In brief, just don't use XsltListWebPart on Application Pages.

And here are some summarized explanations:

XsltListViewWebPart and other OOTB SharePoint webparts (especially complex ones), apparently just aren't supposed to work in Application Pages environment. In other words, they weren't tested there and thus their operability is not guaranteed.

This can be indirectly confirmed by reading at least the following MSDN articles:

• Creating Application Pages for SharePoint
• SharePoint Page Types

.. A site page can also host features such as dynamic Web Parts, and Web Part Zones. Application pages cannot do these things.

Also it is stated in MS course 10232.

Concerning XsltListViewWebPart (XLV) in particular, I heard of multiple problems while using it from Application Page, and experienced some of them myself.

For example, if you customize XLV using XslLink property, XLV will fail to cache the xsl file, and as a consequence, ECB and corresponding buttons on Ribbon will not work. In logs, you will get the following exception message:

Attempted to use an object that has ceased to exist.

Also, you can check out the following question for another example of problems with OOTB webpart on application page (ListViewWebPart, this time):

• Edit or Add ListItem to List in ApplicationPage with ListFormWebPart or DataFormWebpart, but how?