There's a game speed bug that was identified in the MS-DOS version of Flashback (original 1993 release) when running via DOSBox. It normally occurs when the game is configured for Roland music & Sound Blaster sfx. When bugged, the game will run faster than normal speed (70Hz vs 60Hz).
*** If you encounter this bug, you must take steps to avoid it. Any run not performed at normal speed (60Hz) will be rejected. ***
I created a video to demonstrate this bugged speed. Please read the full video description for details:
The workaround is to modify your DOSBox config's autoexec script (or batch file) to run the FB executable 2 times in a row. If the bugged speed is observed the 1st time, quit the game from the main menu and the game will restart instantly. Then, verify that the game speed is normal.
If you are having trouble, you can reply here or contact me directly to help work out the issue.