The robotic arm is only physically capable of holding one disc at a time because it is designed to hold only the standard thickness of the media. However, there are a few things that would cause discs to stick together. 

New Media. New media taken directly from its packaging will often stick together. This happens because the printable surface that is applied to the discs before they are packaged was not completely dry. It is possible for a stack of 100 discs to have 25 stick together at one time. To prevent this from happening, shuffle the media before you place it in the bin to make sure none of it is sticking together. The Bravos have safeguards built in that check if more than one disc was picked.  The job is stopped if this occurs so the user may intervene.

Static Electricity. Static electricity can also cause media to stick together in dry environments. This problem is especially noticeable if you have more than one media brand or type in the bin at the same time. At the point where the media transition occurs it is likely that the 1st brand of media will be statically attracted to the second brand of media. To prevent this, avoid mixing media brands and run the equipment in a climate-controlled environment.

Preprinted Discs. If you print your discs before you burn them and if the media was not fully dry when it was stacked, the ink from the top of one disc may stick to the bottom of another. This doesn't cause noticeable problems with the print quality but it can cause the discs to stick together.