Murder She Wrote was a hit for Nine in 1988, but Nine then lost the rights though they continued to show repeats in the regular 8:30pm Thursday timeslot in early 1989. Ten which had acquired the rights to the new episodes in 1989 decided to screen them up against the repeats on Nine at the exact same time of 8:30pm Thursday.
In checking the SMH archives to check my memory, a 1989 SMH article about Murder She Wrote mentions that in late 1988 repeats of Simon Townsend’s Wonder World were showing on both Ten and Nine in Perth.