Series B and after is the key. Keep in mind, founders generally spend years working on their own dime before getting a minimal salary until (take your pick) revenue of X, profitability, or the acceptance of their first born into Harvard/Stanford etc. Sometimes, the salary increases have not kicked in even at Series B or later.
Another advantage of allowing founders to partially cash out is that the Series B investors get a bigger piece of the company without diluting the Series A or Angel investors.
It is not all that strange, nor should it be construed as problematic. Like everything with start-ups, it depends on the situation.
Good luck getting your partial cash out. :)