Not sure if it is a bug or just intended, but it's still weird behavior.
If you don't enter anything in slider input (so leave it blank), then press left click to confirm it. It changes into VAL when it should just go to the minimum slider value as you have entered nothing or something invalid.
It's not a big deal, but it seems to cause some slowdown when trying to leave the shipcore/build block, or switching to ship mode.