Update...  I am doing an Entity Relationship model and the behavior I'm describing is in the Entity shapes.  It seems that simple Text shapes do allow tabs.  But the question remains why won't the Entity shapes allow tabs?

The Entity shapes seem very quirky and inflexible.  For example why can't I customize the line spacing?  I am short on space and I want to reduce the line spacing but cannot.

Hi Tom thanks for reaching out and I'm sorry for any trouble! Yes when using tab in an ERD shape it will push to the next line-- this is meant to help users quickly fill out the entity without having to manually click each time. I apologize for any inconvenience that causes for your workflow. If adding a normal tab feature for these shapes would be useful to you you can pass that suggestion along to our product teams by adding your idea to our product feedback space. Feedback discussed here is considered when they plan out what to add to Lucidchart in the future. Thanks again for reaching out and for your feedback!