Values in Customizer overridden if slug starts with 'widget_'

[clintstegman]

Any / every Customizer control that starts with 'widget_' is given a value of 'Array'.

If it is a text field, the text field is still valued 'Array', but shows [object Object]

This was very unexpected behavior. If WordPress is actually supposed to be this way, is there a list of forbidden slugs somewhere?

[ocean90]

Duplicate of #36559.