At the following page Pentaxforum.com recommends different Pentax and other gearas. Among all there is a section about Remote control F and says: "In B exposure mode the camera can be set so that the first push of the remote's button opens the shutter and the second push closes the shutter."
According to my experience this information is not valid. I have this very useful device and have tried it on Pentax K10D. It does not stop the shutter open in the B mode. It just fires the shutter in whatever mode including B mode. This information is thus invalid at least when it concerns Pentax K10D. I doubt if this information applies to other models either. Pentaximaging.com at this address does not confirm your idea about the B mode:
PENTAX Remote Control F - Official PENTAX Imaging Web Site
For getting the advantage of using a remote control for B mode you have to obtain the CABLE SWITCH CS-205 which is discussed at Pentax imaging's website.
Recommended Pentax Gear - PentaxForums.com Recommended Pentax Gear - PentaxForums.com
Please be more careful about the information you give here.
Thanks,
Mojtaba Talaian