I think there may be a misunderstanding. Highlighted images by default are not selected. Files, selected in FastRawViewer, have a checkmark in the upper right corner of the thumbnail.
By default, FastRawViewer uses 'Advanced' selection mode, preventing an accidental click from destroing the selection and also allowing to exclude the current file from the selection. This mode is more convenient if the files to be selected are not adjucent, too.
I have multiple selected images showing in ACR/Photoshop filmstrip (vertical, on the left on the screen) correctly. Please make sure your filmstrip is not squeezed to zero width.
Dear Sir: