A block that establishes a new formatting context is pushed by floats.

Source/core/layout/LayoutBlockFlow.cpp

Index: Source/core/layout/LayoutBlockFlow.cpp
diff --git a/Source/core/layout/LayoutBlockFlow.cpp b/Source/core/layout/LayoutBlockFlow.cpp
index fe9339df5d8e2767186d1a764933139a4662d2e6..dcabec7d48e55105f03445b8b3f3a7d08393646f 100644
--- a/Source/core/layout/LayoutBlockFlow.cpp
+++ b/Source/core/layout/LayoutBlockFlow.cpp
@@ -473,7 +473,7 @@ void LayoutBlockFlow::determineLogicalLeftPositionForChild(LayoutBox& child)
     LayoutUnit newPosition = startPosition + childMarginStart;
 
     LayoutUnit positionToAvoidFloats;
-    if (child.avoidsFloats() && containsFloats() && !flowThreadContainingBlock())
+    if (child.avoidsFloats() && containsFloats())
         positionToAvoidFloats = startOffsetForLine(logicalTopForChild(child), false, logicalHeightForChild(child));
 
     // If the child has an offset from the content edge to avoid floats then use that, otherwise let any negative