I'm going to take a little brother, don't I find a bug in PHP? Calculate the last day of the next month related issues

I'm going to go, did I find a bug in PHP? Calculate the last day of next month's problem!
Words not much to say, directly on the code:

$BeginDate = "2015-05-31";
New gets the last 1 days of the specified month
echo Date ("Y-m-t", Strtotime ("+1 months", Strtotime ($BeginDate)));

Based on experience, the results should be: 2015-06-30

But the actual operation result is not, everybody please try, and ask everybody this is why ~ ~ ~ knocked Me Out

Another: If the start time is set to 2015-05-30 the calculation result is correct
------to solve the idea----------------------

$BeginDate = "2015-05-31";
echo Date ("Y-m-d T", Strtotime ("+1 months $BeginDate"));

2015-07-01 on 31

What's the problem?
May 31 plus One months (June is 30 days) so that's July 1, the last day of July is 31st?
Looks like something's wrong with your experience.

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