Well, let's talk about the word until and what it meant in the original Greek. It is the Greek word heoce.

Strong's Greek Dictionary defines it as follows:

heos (heh'-oce);

• of uncertain affinity; a conjunction, preposition and adverb of continuance, until (of time and place):
• even (until, unto), (as) far (as), how long, (un-) til (-l), (hither-, un-, up) to, while (-s).
  

This is precisely the same Greek word used elsewhere in Scripture. In the Greek Translation of the Old Testament, which was prevalent during Jesus' day, we see the following text in 2 Samuel 23

23 Therefore Michal, the daughter of Saul, had no child unto the day of her death.

2 Samuel 6:23

Notice the word unto — it is the same Greek word hoece, this time translated unto as opposed to .

• Does this then mean to imply that Michal had children after she died?

No, clearly it does not. The point is: that while in English, the word until implies something happening afterward, in the original language, the word hoece does not necessarily imply the same.

Lets look at another verse.

24 Then comes the end, when He delivers the kingdom to God the Father, when He puts an end to all rule and all authority and power. 25 For He must reign until He has put all enemies under His feet. 26 The last enemy that will be destroyed is death.

1 Corinthians 15:24-26

This verse is talking about the reign of Jesus. Look at verse 25. If we insist that the until in Matthew implies that Joseph knew Mary after the birth of Jesus, then this must mean that the reign of Jesus must come to an end after He put all His enemies under His feet.

Now I don't think any Protestant wants to go there!!