Close tab minimises project sidebar

If I have multiple files open and decide I want to close a few of them, for whatever reason, as soon as I hit the Close keyboard shortcut it closes my project sidebar instead of the next file.

For example:

Press CMD + W to close the file (file closes as expected)

Press CMD + W again to close the next file (project sidebar closes).

I've checked and I only have CMD + W assigned to Window > Editor Tabs > Close. I have Ctrl + B assigned to opening/closing the project sidebar as indicated here:

Is there a way to turn off this behaviour?