Get-ChildItem with -LiteralPath is throwing "The specified wildcard character pattern is not valid" when filenames contain brackets

Question

I'm trying to get a list of folders in a hierarchy that don't contain any mp3 files. (The goal here is to eventually clean up all the "empty" folders that only have album art, thumbs.db, desktop.ini, etc. files left). So I wrote a quick PowerShell
command to try to do this. But it doesn't seem to be working.
I already checked out this thread <Get-ChildItem
SomeFile[].txt occurs error because of the [brackets]: "specified wildcard pattern not valid"> and I think I'm using LiteralPath correctly. Any other hints for troubleshooting this problem? Here's the command I'm using.
Get-ChildItem -Recurse -Directory | ?{
@( @(Get-ChildItem -LiteralPath $_.FullName -Recurse) | ?{
$_.Extension -eq ".mp3"}).Count -eq 0 }
This is on the latest version of PowerShell found in Windows Technical Preview.

Answer 1

Fair enough, but it still doesn't answer the original question- why isn't this working with -LiteralPath when the path contains brackets? 
Get-ChildItem -Recurse -Directory | ?{
@( @(Get-ChildItem -LiteralPath $_.FullName -Recurse) | ?{
$_.Extension -eq ".mp3"}).Count -eq 0 }
Thanks,
Ben