Hi @Carsten4207! That's a great question!
The vast majority of the fixes are in the system firmware so updating your photon with the new system binaries will bring in those fixes. Examples of these are I2C stability, TCPClient stability.
There are a handful of fixes that are in the application firmware part and these require rolling out 0.4.4 to Particle Build. (Examples of these are floating point "%f" support in
WiFi.selectAntenna() and Wire.setClock(CLOCK_100KHZ`) All of these are compile-time issues (code using those features will presently not compile, but will compile once 0.4.4 is deployed to Build.)
The WebIDE will not revert your system firmware, so you'll still have all the fixes in the system firmware even though your application code is compiled against 0.4.1. When 0.4.4 is released and you build an application against 0.4.4, the Cloud will upgrade your system firmware automatically over-the-air to 0.4.4 if it's at an older version.