SQL Server is a widely used product that has been around for many years. It is generally stable and usually behaves reliably and as expected. But, like any large software application, it has it's quirks - these are often the result of the particular implementation approach taken by the SQL Server development team. Quirks are not necessarily bugs - a bug is something that is wrong whereas a quirk is simply something to be aware of.
Listed below are some of the quirks that I have come across during my SQL Server work, none of which are commonly known, or at least widely reported online.