Hope there is problem with the creation of the XSLT web part. I am not familiar on how you create the XSLT web part. Here i provide a procedure for creating the XSLT web part(Which i Use).
1) Add a new web part zone found in ribbon using the Sharepoint Designer
2) On Insert ribbon you can find DataView dropdown Click and add Empty Data View
3) Now You can find a empty data view is added to the web part zone.
4) In the Empty Data view You can find Click Here to select a Data Source link available. Click it and choose the source of the data
from which you wanted to add details Either List or Library.
5) Now on the Data Source details available on the right bottom corner you can find a button named "Insert Selected Field as.."
Click on it and weather you want to add single Item View or Multiple Item View.
6) Now on the Ribbon available on Options you can find Add/Remove Columns button. Click that.
7) Edit Columns popup will be available and you can find 2 sets of fields were available
i) Available fields and
ii) Displayed Columns
8) Delete all the fields available in the Displayed Columns and Choose the fields you required from the available fields.
9) Click ok and you can see all the chosen fields available with the XSLT Web part.
Hope this helps.