Embarrassing story...

We ran out of shortcut keys, so we have implemented a dual hotkey system for some keys. It's not a new concept, it is used by a few companies, but is not widespread.

The idea is that you can hold a modifier key and then press one key then another key to complete the action

So in this case:

B will splice
Alt b, Alt s (will do what you want)
Alt b, Alt e (Really cool and will blow your mind) - check the Overview docs for 2019.1 for a description ;-)

So hold down alt, press b then press s (while still holding Alt)

Right click menu below to show how to do it from the library and also showing the updated shortcut.