The screen shot shortcuts ⌘ Command ⇧ Shift4 or ⌘ Command ⇧ Shift4 do not write a file.
The latter shows the cross hair and let me define an area but that's it.
Copy to clipboard works for both screen and selection area. Grab can write a file too.
The issue occurs only with my user account but not with another (I created an new user to narrow down the failure area). My humble conclusion is that it must deal with my specific environment/configuration, but I have no clue how to narrow it down further or pin-point to the error prone configuration:
System preferences → Keyboard → Shortcut does not give any hint: No error no warning.
Both shortcuts are assigned to the two system functions "save picture of screen as a file respectively save picture of selected area as a file.
I did disable/enable the checkbox, too; no effect. I changed the target directory forth and back and restarted the UI Server; no obvious effect.
Any idea how to figure out the root cause or better, how to fix the problem?