Most often in the past, when I've heard reports such as this, the issue boils down to factors such as ad creation date, and the date range that is being looked at. For instance, here are a couple of typical scenarios:
* If the two ads were created at different times, then the stats below them will reflect that timing difference, and are not likely to be exactly 50/50.
* If the ads were ever allowed to be 'automatically optimized', and then were later changed to have even distribution - the stats will reflect the earlier 'optimized' percentages if the date range includes any time at all when they were not showing evenly.
With all that said, Robsp, if you've noticed a case where ad rotation is not operating correctly, please feel free to contact support and have them take a look.