This issue was marked as a duplicate of UE-48194, which is in turn a duplicate of UE-47843. Please refer to those bug reports for further information.
Opening a blueprint that has an input event in it cause the blueprint to become dirtied and require compiling.
This did not occur in 4.16.3-3561208+++UE4+Release-4.16
4.16.3-3561208+++UE4+Release-4.16 - Did not occur
4.17.0-3573198+++UE4+Release-4.17 - Occurred
4.18.0-3575318+++UE4+Main - Occurred
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