I am on the preview testing cycle for Windows 10. Why? I like to be tortured I guess. Originally, it was to get an early view of the OS through the Windows Insider Program.
At one point I installed the released version but the program overlaid my full OS with another build of the Preview releases. You have to cancel the program to prevent this.
I received build 14251 as part of the normal sequence but I found this release broke jabber. The text was invisible. Secret Agent Man Font? I verified many things were in place (an old one is active scripting disabled for IE). But nothing readily obvious.
A few days later 14257 was released and jabber worked again.