Problem hope someone can solve

Regarding standby radios in FS 2004. Aircraft like the B 737 have
standby radios which work as real rados do. Other aircraft loke the KA
350 do not have SB radios but when U add them they work backwords. When
U try and chamge the standby frequency, the active frequency actually
changes resulting in only one radio and really no standby.

Any solutions for this problem. Seems in some aircraft when U add stand
by radios they work fine

Tks for any help, solutions

PJ