• open fileA.ts that exports a symbol that is used in fileB.ts
• rename a symbol in fileA.ts
• (fileB.ts opens as a background tab)
• save all
• hit the x on the fileB.ts tab
• observe (through logging) that fileB.ts is not disposed

Now do the same steps, but first click on the tab with fileB.ts before hitting x. Now, fileB.ts is disposed.

Notice how fileB.ts and fileC.ts do not get disposed:

Notice how fileB.ts and fileC.ts get disposed now: