There's a few bugs in the latest stable version.
4.1 or 4.2 did have a problem that caused some plugins to simply disappear without a trace. Thankfully that was fixed.
There's some Mac users having trouble even getting it to launch, but I think you're on Windows.
The only current bug I'd consider "unsafe" on Windows is that under specific circumstances garbage data might get written to one of the config files and cause the built-in Open With to throw an error. Kovid stomped that bug, just don't add any new applications to that menu until 5.4 comes out.
Some minor bugs too that are just annoyances. The search in the Annotations Browser broke, composite columns with checkmarks showing red Xs on everything, etc. Occasional plugin bugs when a bit of code doesn't get along with newer functions.