I too have experienced this problem. I have narrowed it down to the two CR+LF that the apache web server seems to put at the start of the response when processing the jsp file. I can sucessfully call a straight html file, a response generated by php, and even the response generated by a jsp if a pass it through a filter to strip out the extra CR+LF at the start of the response.
If you just call the data provider with a browser and look at the source you can see the extra characters. It seems 4.5 can handle these OK but ovsd5.1 can handle this white space.