When you connect an output port to an input port of a different type, a small ("collapsed") node called a type converter is inserted.
Sometimes you might want to use a type converter node without it being collapsed, for example if trying to connect it to multiple output ports. This screen capture by @Bodysoulspirit (https://vuo.org/comment/2836) demonstrates with the
Mix Audio Channels node as the type converter: Auto Shrink.mov.
So, instead of always collapsing a type converter when it becomes connected on both ends, only collapse ones that were automatically inserted from a cable drag, and never collapse ones that were manually added from the node library.
Workaround until this is implemented: Connect the type converter node's output port to multiple input ports before connecting its input port. This leaves it un-collapsed.