ps- i was right, just FYI. i see this all the time and it's starting to drive me bonkers. according to the book:

Enclose parenthetic expressions between commas.

The best way to see a country, unless you are pressed for time, is to travel on foot.

This rule is difficult to apply; it is frequently hard to decide whether a single word, such as however, or a brief phrase, is or is not parenthetic. If the interruption to the flow of the sentence is but slight, the writer may safely omit the commas. But whether the interruption be slight or considerable, he must never omit one comma and leave the other. Such punctuation as

Marjorie's husband, Colonel Nelson paid us a visit yesterday,

or

My brother you will be pleased to hear, is now in perfect health,

is indefensible.