MSL_MANI wanted to know, how he can DESELECT one poly (which is mistakenly selected). This is done with a workaround. Just use the undo-function (which works well for Deselecting the last few selected polys), or use "select inverse", now select the not wanted polys, the again use "select inverse" -> then it's done.

I've asked the support a while ago and got this nice hint

With CTRL you can select multiple polys