Either it's a bug or a limitation. Haven't yet tried this, so I can't tell you whether it works as it should or is acting up... I would however assume that within what one can expect it works as designed - ACR doesn't have a built-in timeline, so there would be nothing for the PS routines to request retrieval of frames from withing the SO.
You might be correct that this is not a bug. I just tried some other random filter and it worked the same way when used on a video layer. However, when i use non-destructable adjustments, then they will be applied to the whole clip. That's why i assumed that filters would work the same. Otherwise filters are quite pointless to be even possible to use against video layers.
Have you tried converting the video group into a Smart object? OK, I thought I'd better check, and it works for the entire clip(s) when converted to a Smart Object, but as the OP says, only the first, or whatever frame was active when the filter was invoked, when not as a smart object.