This is not a bug, but it's true that it is a bit ambiguous. In-game there are places where you get information about the recovery speed and places where you get information about recovery time.
The relation between these 2 concepts is that they are the reverse of each other: recovery speed=1/recovery time. The tooltip for DEX is related to recovery speed (it also affects attack speed, reload speed, cast speed but these are not relevant now), therefore you have an increase of 30% to your recovery speed. Applying the formula above you get the the time you get to achieve full recovery, recovery time, is 1/1.3=0.77. Therefore, your recovery time, as displayed by the weapon tooltip, is reduced by 1-0.77=0.23. So an increase by 30% in recovery speed equates to a decrease of 23% in recovery time.
kmbogd's post in [Attributes] Dexterity not calculating correctly? was marked as the answer