AdobeRGB has a wider gamut, preserving more information, meaning more headroom for editing. The problem is that not all web browsers read the colour space field in the jpg. This makes for a dull, lifeless rendition. The same thing happens when sending a file out for printing, unless the copyist know what he/she is doing. sRGB is a safer option when you don’t have full control over all steps between your computer and the viewer’s eye.
I have no idea what can have brought on the sudden change in behaviour in your camera. Within the PASM group, nothing should change the colourspace, but the automated modes usually override your settings and switch to the safest space…