delay problem

Hi there！

I will be very grateful if someone solve my problem. It's seem to be a basic problem, however I cound't fine a proper way to explane it. I am very wondering why.

Program:

-----------------------------------------------------------------------------------------------------------

module Tfine(clk_50M,clk,clkPLL,SampleClk,trig,stop,push,t,s);
input clk_50M,push;
output clk,clkPLL,SampleClk;
output reg trig,stop = 1'b0;
wire HIGH = 1'b1;
wire LOW = 1'b0;
output wire t,s;

PLL p1(.refclk(clk_50M),.rst(LOW),.outclk_0(SampleClk),.outclk_1(clk),.outclk_2(clkPLL));

assign t = (~push)&clkPLL;
assign s = t&clk;

always@(posedge t)begin
if(push == 1'b0) trig = 1'b1;
else trig = 1'b0;
end

always@(posedge s)begin
if(push == 1'b0) stop = 1'b1;
else stop = 1'b0;
end
endmodule

-----------------------------------------------------------------------------------------------------------

Waveform on signal tap:

-----------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------

My problem is I don't know why there is a delay between posedge clk and signal s. I use a similar way to descript s and t. When clkPLL rise, t will rise immediately. However, I cound't got a same result on t.