The Bug:

Desert Temples can override bedrock except the last layer of bedrock.

Steps to Reproduce:

1. Create a normal world with this seed: 2482490754905255652
2. To help you see the bug, run this command: /effect give @p night_vision infinite
3. Teleport to the following coordinates: 10 -63 10
4. You will notice you are standing on the last layer of bedrock:  
5. This step is optional. Break all the sandstone and its variants you can reach without modified attributes in creative mode, and do not move from this point until the step is done. 

Expected Results:

No desert temple should replace bedrock blocks.

Observed Results:

Desert temples can seem to override most bedrock in rare cases. If you broke the sandstone you can reach in step 5, you may notice there is no bedrock in places where it may have supposed to generate: