My first post! How about that!
I agree with Gary and would add the words of the old maxim:
"Don't assume - CHECK!!"
Of course, there are ways for an ATCO to minimise confusion by adding things like "Maintain runway heading until advised" or words to that effect. However, very often, additional phrases like that are not standard phraseology and therefore may not be used, so if you are not sure, ask the controller.
Finally, if it was me going to give you a rebuke, believe me, you would know it!