The Bifrost rod recharge time seems to be linked to when the rainbow bridge disappears.
However when the Bifrost rod is thrown on the ground after use it stops charging. This does not effect the rainbow bridge and it disappears as normal.

Using latest forge, Baubles and Botania version R1.1 74

Also I noticed that I can middle mouse click to select the rainbow bridge block in creative.

There isn't much I could do about the one regarding dropping it on the ground, but I'll fix the pick block one since you aren't supposed to have those blocks.