Tabs in Timeline panel disappear sometimes

I use the tabs in the timeline panel to jump back and forth between opened/active sequences. But occassionally, all the tabs will suddenly be gone. I can still find the opened sequences by clicking on the >> dropdown to the right of where the tabs used to be, but that's fiddly.

If I change workspaces, the sequence tabs are suddenly all open again in the Timeline. It's an easy fix, but takes 10-20 seconds as the program switches workspaces.

It used to happen quite frequently, multiple times per day, but lately it's only occured once every few days.

Is this a bug, or something I'm triggering by accident?

Tabs present 

Tabs disappeared