KalleL:
But I must admit I am surprised the Arduino software people have let through a
bug like that ...
Really? Even Microsoft has not supported Windows XP for more than two years:
"After 12 years, support for Windows XP ended April 8, 2014"
Why should Arduino spend time and money testing and supporting the IDE on an unsupported OS? If you want Windows XP support you could always try the last released version from before Windows XP was put out to pasture: ARDUINO 1.0.5-r2 (2014.01.08). If you don't mind running beta-test software you could use ARDUINO 1.5.6 BETA (2014.02.20).
Also, the change is in the linker which is not something Arduino develops. They just occasionally include the latest version in a release to get the benefit of bug fixes and new features.