The bug

It is possible to use a spawn egg in such a position that the spawned mob will immediately begin suffocating, or in similar invalid states such as intersecting a block. This is inconsistent with other items which create entities, such as armor stands and boats, which refuse to be placed unless their usage results in a valid state.

How to reproduce

1. Create or encounter a one-block-high setup similar to that shown in the screenshots attached
2. Attempt to place an armor stand in this one block high region
3. Attempt to use a creeper spawn egg in this one block high region

Expected results

As armor stands and creepers are both greater than a block high, neither would be able to be placed inside of this one-block high region as it does not have sufficient space to accommodate them.

Actual results

The armor stand is correctly blocked from placement. However, the creeper is allowed to spawn in this invalid configuration and immediately suffocates as a result.

Further notes

This is not a duplicate of MC-103934; that ticket concerns the fact that mobs can suffocate in otherwise valid positions (or positions that can be easily be made valid) when a spawn egg is used, whereas this ticket concerns blatantly incorrect positions.