Two students (Laura Grupp & Michael Wei) for the Non-Volatile Systems Laboratory at UCSD found this:
Our results show that naïvely applying techniques designed for sanitizing hard drives on SSDs, such as overwriting and using built-in secure erase commands is unreliable and sometimes results in all the data remaining intact. Furthermore, our results also show that sanitizing single files on an SSD is much more difficult than on a traditional hard drive.
That is not good, you can read the full paper on the subject here — this link takes you to the much more digestible synopsis. From what I can gather this is not widespread and is a result of defects on the manufacturing side — meaning this may or may not effect your SSD.