When developing Dynamics AX7 with Visual Studio a handy little helper is IntelliSense.
But no matter which language is used (AX7, pure C#, etc.) sometimes I ran into the following problem:
IntelliSense does not select the default item anymore when popping up the list:

As you can see in the screenshot, the first line is blank, but I expect it to show the default selection like here:

The reason for this is the key combination CTRL + ALT + SPACE!

This switches the impact modes of IntelliSense (between low impact and high impact mode).