The Translation card allows users to switch the default translation service (Apertium, source text, nothing, etc.). When the user changes it, it only applies to the next paragraph.
In addition to keeping the selection for next paragraphs, it would be expected for the selection to take effect on the current paragraph too.
This is especially relevant when MT is disabled by default for some language. When the user selects the MT provider nothing will happen which make it hard to use MT in the first paragraph.