In 2010 My PRO stamped Qatar RP even there was a valid visa of Sharjah in my PP... (profession in sharjah RP was civil engineer and Qatar RP stamped labor, later i changed my profission)

i think it is just if immigration official go thru your PP pages.. or may be by chance... but i also heard in 2009 some people cancelled their existing RP to get Qatar RP...
But there is also a provision in Qatar labor law that a professional can have multiple RP's but with different fee structure.. may be one has to pay more than QAR 1000.
you do not worry enter Qatar and finish all procedure and try... Good luck...
in Qatar there is daily new laws...