Indeed, seems like button handling is messed up here...

This seems like a very typical use case of custom gizmos so definitely something that should be fixed for 2.80.

Two notes:

• This bug seems to have been there since 2.5, I think since rB6634ed9a872ac. (Testing 2.5 Alpha, the issue is present there.) In 2.8 it was quite difficult to replicate without the given .blend file.
• There's still an issue remaining for 2.8 here: Before clicking "Back to previous", the fullscreen of the newly activated Motion Tracking workspace is corrupt. Except of the global bars, no redraw happens, all regions are regarded as hidden. Checked a bit but not sure if I'll have enough time to fix this. It seems the fullscreen area vertices aren't scaled correctly, making it too small for any regions.

5. The operator settings region in the bottom left often has the wrong size, and is way too big.
   • We could make the area size dynamic, based on the number of options:

Requested information not provided after a while. Closing due to our tracker policy.
If requested information is given and the issue still persists, we can reopen.
Thanks for reporting nevertheless.

Think this is fine, although better wait until it's used somewhere else than file browser (outliner most likely). Also, might make sense to add UI_ prefix, so UI_SELECT_WALK_FOO to make clear this is UI only.

I realize this only aims for basic support. However for more than that I'd like to leave some notes here.

Discussion about the general file browser design should go into T62971. A colleague and I are actually working on this so expect news soon.
I'd vote for removing the '..' entry. For some users it might be confusing, and there is a button and a shortcut for it (P). With the button moved close to the file path, as planned, I think that will become more discoverable.

@Jeroen Bakker (jbakker) you should probably double check how I resolved the merge conflicts ;)

Fixed the file browser glitch too now (rB0a28bb14222c).

Committed fix for the crash now.
For the record, I'm sure this used to work, Campbell and I both worked on getting fullscreen file reading with workspace versioning to work fine. So this must have gotten broken by some further changes somewhere. Shows once more how fragile the full-screen code is...

Just for the notes: What's there now is not the final design. @William Reynish (billreynish) already started working on a design to edit this configuration from the new Preferences. I hope to get around to implement this soon.