I have number decimal type in database and have a required field for that. Iam using regex ^\d*\.?\d*$ for this field.
As a result, it refuses to save single zero number. No javascript alert on the filed, only "Warning Invalid field: My Decimal".
All other numbers like 1-9 or decimal 1.2 etc. are ok.
But when I remove "required" for this field it works and it will be saved.
Tested in sandbox.

This is not fixed since 2.7