Almost any Vocal Remover too assumes the vocals are centered in the mix. This is just how they work .. so they try to find the sound and cancel it (many times by reverse polation as mentioned).

However sometimes the reverb is not centered, and this may be what you notice.
If the L/R reverb is a separate signal, the Vocal Remover may ignore it.

It's one of the main problems with true vocal removal .. I do not know of a reliable solution other than trying other techniques on the result, which often deadens the mix.

It's an art not a science; many times it's not easy, if even possible.

I do not work here, but the benefits are still awesome
Make your sound your own!