Eclipse won't move project. .metadata/.lock is locked

In Eclipse, if you want to reorganize your filesystem, you cannot just move your Eclipse project's files on the filesystem. Instead you right-click your project in Package Explorer -> Refactor -> Move, and select the new path (which I learned from stackoverflow).

However upon attempting this move with the Minecraft Forge Eclipse workspace, I get a "Move Problems" error dialogue with the error message

Could not move /MDKExample

Could not move C:\Users\user\forge-1.8.11.14-mdk

Could not read from source when writing file C:\Users\user\forge-1.8.11.14-mdk\eclipse\.metadata\.lock

The process cannot access the file because another process has locked a portion of the file

After clicking through the dialogue, the source and destination of the moves are both left in an unusable state due to the half-completed move of files. Downloading fresh copy and rebuilding the Eclipse workspace with gradlew setupDecompWorkspace && gradlew eclipse, the move fails every time. And I tried with several different versions of Forge. What is the secret to moving a project's location in the filesystem in Eclipse?

Windows Process Explorer shows that the only process with this file handle is eclipse itself, and after exiting Eclipse I am able to move the .metadata\.lock file (but not before). Why is Eclipse itself blocking the .lock file for a move? I tried creating a new blank Java project with a single Java class, and Eclipse moved it just fine, so is this problem something particular to Forge?

I'm using Eclipse Mars.1 (4.5.1) on Windows 10 with Java 8.