Shift+"." is, unfortunately, the same as ">" on some eyboards, so yes, on those keyboards, they conflict and make neither work. See #34306: Default keyboard shortcuts for staccato and decrescendo cause neither to work. You can reassign one/both of these in Edit / Preferences / Shortcuts. Given the multitude of different keyboard layouts out there, it is next to impossible to find a single set of default shortcuts that will work for everyone, and we haven't quite figured out out how to deal with this.

As for Shift+K (to bring up the key signature palette), that seems to be some sort of issue with the palette code, as when I try it, I get an error message printed to the console window if I have one open (eg, if running under the debugger). Simialr issue with the shortcuts for the time signature and symbols palettes. I keep meaning to look into this, I guess that's my project for this afternoon :-)