In debug mode you should not need to restart, it turns the caching off.
However I've had a play around and I think I see the problem...in the XML the XMLData node is stored as encoded html
<XMLData><genxml><textbox><txttest>TESTtextbox</txttest></textbox><checkbox /><dropdownlist /><checkboxlist /><radiobuttonlist /><edt /></genxml></XMLData>
So xsl will not parse this and hence you have a blank output.
The only way around this I can think of is to maybe use substring-before and substring-after functions on the XMLData node something like this :
<xsl:value-of select="substring-after(substring-before(./P/NB_Store_ProductsInfo/XMLData,'</txttest'),'txttest>')" />