VirtualBox executor's snapshot restore doesn't seem to work reliably

With the virtualbox executor I'm getting this error message at the top of each build that starts immediately after a previous build completes:

gitlab-ci-multi-runner 1.1.3 (a470667)
Using VirtualBox version 5.0.18_Ubuntur106667 executor...
Restoring VM from snapshot...
Previous VM failed. Deleting, because VBoxManageOutput error: VBoxManage: error: Cannot delete the current state of the running machine (machine state: Running)
VBoxManage: error: Details: code VBOX_E_INVALID_VM_STATE (0x80bb0002), component SessionMachine, interface IMachine, callee nsISupports
VBoxManage: error: Context: "RestoreSnapshot(pSnapshot, pProgress.asOutParam())" at line 528 of file VBoxManageSnapshot.cpp
Creating new VM...
Creating default snapshot...
...

The build continues and succeeds so this isn't a fatal error.

At least one other user has seen this too: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/merge_requests/31#note_2656194

I'm using VirtualBox 5.0.18 from Ubuntu 16.04 (Xenial) and gitlab-ci-multi-runner 1.1.3.