I used to believe myself turning from headwind to tailwind would result in a marked decrease in IAS, but this is a common mistake. The only loss in IAS results from increased induced drag during the turn.
No matter how rapid your heading change is when turning head- to tailwind there will be no decrease in IAS. Your airspeed doesn't change in relation to the cube of air you are in, only to the ground beneath you.
In order to understand this fact (and I still doubt myself sometimes) I imagine the cube of air being still and the ground map moving like on a rollerfloor below me. No matter what my heading is the air around me doesn't move and IAS remains the same. On the other hand, my speed in relation to the ground does vary with my heading.