As one of Vuo's developers, I work on Vuo's engine (the thing that makes compositions run), work on nodes, and write documentation. You'll see me on the forums answering people's questions about Vuo.
I've been developing apps and frameworks for several years (since I was in college). Pre-Vuo projects include Kineme Quartz Composer plugins, iOS apps for education, an app that analyzes photographs of tomato slices, and software to help people with disabilities use talking keyboards.
I enjoy using Vuo to make live music visuals. My hope for Vuo is that it will grow into a community of people of diverse backgrounds and identities making lots of different artistic, useful, unique, goofy, beautiful, crafty, wonderful compositions.
The different behavior is meant to streamline the most common usage for each node. For most nodes, the text input editors behave like other types of input editors, with Return accepting the input and dismissing the input editor. For Make Image with Shadertoy, obviously the Return key is essential to editing the text, so Return makes a linebreak and you have to click away to dismiss the input editor. (This comes from the "isCodeEditor":true in the node source code.)
In your first screenshot (where the cable is already connected), the cable from Fire Periodically : Fired to Smooth with Duration : Set Position is a thin cable, called event-only. In your second screenshot (where you reconnected the cable), the cable is a thick cable, called data-and-event. The thick data-and-event cable carries more information than the thin event-only cable, namely the data from the Fire Periodically output port (the number of seconds since the composition started). This data overwrites the data in the Smooth with Duration input port. The thin cable, on the other hand, lets the input port keep its data.
To draw the thin event-only cable instead of the thick data-and-event cable, hold down Shift while dragging the cable.
The same thing is going on in your third screenshot. The cables from Receive Mouse Clicks to Select Latest are event-only, so they don't affect the data in the input ports.
If you want the Select Latest to select between 2D points instead of text, you can right-click on one of its ports and choose "Revert to Generic Data Type" (or drag a new Select Latest node from the Node Library), then drag cables from Receive Mouse Clicks to Select Latest. These will be the thick data-and-event cables, and connecting them will change the Select Latest ports to 2D points.
If you're not familiar yet with the concepts of data and events, there's a lot of information about them in the manual.