BW, Yes, that situation is well documented and not at all surprising; the downwash from a helicopter can be surprisingly intense. There was a tragic, fatal accident at St. Mawgan/Newquay some years ago where the pilot of a light aircraft went around from an approach and its pilot subsequently lost control after allegedly being affected by downwash from a RAF Seaking operating alongside the runway. The RAF pilot was an acquaintance of mine and the burden of blame placed on him was, in the circumstances, unfair. I don't think he ever got over it and he passed away in sad circumstances at a rather young age.
Crab was referring to the other situation, i.e. how turbulence from a fixed wing tends to affect a following helicopter to a far lesser extent.