It is possible for azalea trees & rooted dirt to generate on top of bamboo blocks. In the example below, the rooted dirt is placed at the top of a bamboo. The world was created in 21w38a and the chunk was loaded in 21w41a.
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We're tracking this issue in MC-237500, so this ticket is being resolved and linked as a duplicate.
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Might as well include bamboo in MC-237500.