The condition is not saved in the inbox filter

In Inbox filters by inserting a new rule, when a condition is entered, pressing the '+' key after populating the fields, the entered value is deleted.

Steps to reproduce:

• create a new filter rule
• add a condition
• enter a value
• click the '+' button to add a new condition

Expected behaviour:

• the entered value is saved

Actual behaviour:

• the value entered is not saved

Workaround:
move with the mouse and press an empty point on the screen or press Enter

Thanks to Federico Ballarini (#88097)