Comment # 14 on bug 969768 from Wolfgang Bauer

Ok, I finally was able to reproduce it, by "trashing" my whole music
collection.

But it is not related to the size at all, it just only happens with folders,
even if it contains a single file.

The important point is this though: it (only) happens if you hover the mouse
over a folder in the trash.

It is be related to the preview generation.
If you disable previews for folders in dolphins settings (General->Previews),
the problem doesn't happen.

Btw, in case you didn't know, you can also bypass the trash by holding down the
Shift key when choosing "move to trash", then the things are deleted directly.
You can even activate a "Delete" context menu entry that bypasses the trash in
dolphin's settings.