Clarify the issue (closes: #16975)

wiki/src/support/known_issues.mdwn

@@ -460,8 +460,8 @@ Tails does not erase video memory
 
 Tails doesn't erase the [[!wikipedia Video_RAM_(dual-ported_DRAM) desc="video memory"]] yet.
 When one uses Tails, then restarts the computer into another operating
-system, that other operating system can see what has been displayed on
-the screen within Tails.
+system, that other operating system might, for a moment, display the last
+screen that was displayed in Tails.
 
 Shutting down the computer completely, instead of restarting it,
 might allow the video memory to empty itself.