@carlos reasoning seems to be supported by the fact Spain's productivity is going up after all the low skilled workers in construction were sacked.
Some of the comments of the FT are highly interesting.
I'm not saying that productivity is going up, it's in fact going down, as the article says -3.1 variation GDP 2008-2009. But the ratio of unemployment/varGDP is very different to other countries because of the additional unemployment from construction industry, which is the suspicious indicator used by the author.
In any case I personally agree with some of the comments in the FT article saying that Spanish government may artificially modify some figures.
I missed the productivity data in the report (I found only production output) and FT just took out the report from the web.
The question is not that the Spanish government did modify some figures, but if the modifications were in line with countries like Greece or like Germany.