The Delete button in the TSA dialog should be disabled when no entry is selected.
The dialog is found in Tools - Options - Security - TSAs
Created attachment 132331 [details]
Time Stamp Authority dialog, delete button active with focus
Sabin Frandes committed a patch related to this issue.
It has been pushed to "master":
tdf#106945 TSA Dialog: Disable delete button
It will be available in 6.0.0.
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.