The [SEND FX] effect sound is output even though it's not sent. Why?

Depending on the type and settings of the selected effect, the effect may remain.

Check the following.

■When [TAPE ECHO] is selected with the SEND FX selector switch

Effect sound won't be decayed to zero while feedback amount is set to somehow large by [PARAMETER] knob. 

■When [EXT] is selected with the SEND FX selector switch

Check the settings of the connected external effects unit.