SD card reader problem

I have a Macbook Pro mid 2012 (9.1) I7, with 8GB RAM and running Mavericks 10.9.4. On two separate occasions, when inserting an SD card, it showed up on the desktop as "My Book" and appeared totally blank. The first time it was a Sandisk 32GB card from a Nikon D800E, the second time, months later, it was a Lexar 32GB card from a Fuji X T-1. On both occasions I was able to recover the images with recovery software. I have used the same cards multiple times in both cameras with no problems. Based on this I have to assume that whatever this intermittent problem is is with the computer since it happened with different cards from different cameras and 4 months apart. It's a bit nerve racking when this happens even though I have purchased effective recovery software. Any suggestions would be greatly appreciated.