Interrupted only when I tend to digress (6,2)

'interrupted' is the definition.
(butting in is a kind of interrupting)

'only when i tend to digress' is the wordplay.
I cannot quite see how this works, but
'only' could be 'but' (but can mean only - eg 'life is but a dream') and 'but' is present in the answer.
'i' is found in the answer.
an anagram of 'tend' is 'tedn' which is present in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?