Space or no space for (instrumental) tracks?

[steveotron]

This has always bugged me, and is there really any standard convention on the "official" way to write/tag these tracks?

The CD jackets do not appear to have a space between that track title and the "(instrumental)," so which would be considered correct?

track(instrumental)
or
track (instrumental)?

EDIT: forgot my example.

The lack of a space is pretty much consistent for all the K-ON! releases, and it's quite common for other releases too (example 2).