A weird encode character returned from Page.ClientQueryString()

Here is the input query string that I enter on the Address Bar:

https://myapp.com/myproject/exagoviewer.aspx?act_code=R&rep_own=AAAAAAAAA&report_name=3.52%20SR%20-%20Request%20Time%20Analysis&report_code=3.52%20SR

Then, in my code, when I get its query string by calling Page.ClientQueryString(), it returns this string

act_code=R&rep_own=AAAAAAAAA&report_name=3.52+SR+-+Request+Time+Analysis&report_code=3.52%2520SR

You can see there is a weir encode string in the parameter report_code=3.52%2520SR, it should be report_code=3.52%20SR

Then I tried calling another method HttpContext.Current.Request.Url.Query to get the query string, but I got the same issue:

?act_code=R&rep_own=AAAAAAAAA&report_name=3.52+SR+-+Request+Time+Analysis&report_code=3.52%2520SR

I have no idea what the problem I am facing now. Any advice, please?