Dynamic Map Service Layer fails to display after Tiled Map Toggle

[BenSayers]

Hello,
I have created a combination of the two JSAPI examples: Toggle Layer Visibility  and Toggle multiple ArcGIS Online services

The problem is that when I switch the Tiled layer services (basemaps) the dynamic layer on top disappears. I have tried re-adding the dynamic layer to the map after the basemaps are switched but this doesn't work.

Any help very much appreciated.

Many thanks,
Ben Sayers