Whether the door latch is stuck open or closed, you need a way to get your door functioning correctly. There are several possible issues and potential fixes that you can attempt yourself or you can call a professional.
There is no real difference in how the latch moves when it is pressed in, and when the handle is turned (both when the door is open and closed). This has to do with a build-up of material within the components, which allow the latch to extend and retract as a result of hindered spring tensioning.
What is happening? Due to moisture, rust can collect inside the lock as well as on the latch bolt, this creates needless friction as the metal bits of the lock try to slide past one another or get out of the way of other moving parts. This can obstruct the movement of springs as well.
Solutions! In these cases, it is always best to disassemble the lock and do a bit of cleaning. Letting the mechanisms sit fully submerged in vinegar of about 5% acidity will do the job of separating the muck from your metal. Rust removal is very common in older homes where you may see many mortice locks. It’s something that affects all locks given enough time, but after about a day of sitting in the vinegar the locks can be wiped down and polished, which will make them look brand new. Besides just wiping down the finish, you may also need to scrub out certain nooks and crannies with a small brush.
How you polish the lock will determine how swiftly the lock will rust again. It’s a good idea to use something like car wax to seal all the small imperfections in the metal that are prone to future rust. Before applying any polish, take time to dry the lock components, once the polish has completely coated the lock, ensure you remove all excess polish to avoid causing the latch sticking.