I am almost certain this used to work differently.

In a Project, in a custom Integer field, we can click into the field and enter a value, then press Tab to move to the next field.  But, doing so will not actually update the value until you click somewhere outside the field with your mouse.

Further, if you - for example - Tab through several fields and enter values, then click outside the field to cause an actual update, only the first field you updated will be saved, the others will be reset to their pre-update value.

I don't think this is the intended behavior.