Bulldog,
It is very common in pitchers and it tends to provide some degree of protection for the elbow simply because the elbow can't hyperextend as a result.
It can happen as a result of tissue contraction such as you've noted after weightlifting and can also happen as a result of loose bodies or bone spurs in the posterior elbow. Both can become permanent and conventional wisdom is that it doesn't impact performance until it reaches about 25 degrees of extension loss which is quite unusual.
It isn't a matter of taking care of the biceps enough given what a high percentage of pitchers have some degree of extension loss.
Pitchers will see a temporary extension loss immediately after pitching but in most cases it recovers in a day or two. Pitchers also tend to have their extension loss increase over the course of a season when it is due to tissue contraction and it then takes a fair amount of time off to recover the extension. Sometimes it becomes permanent.