"Stacked" motion blur

Hello,

I have my particles starting at frame -240. At frame 1 the Eevee render looks like this:

It’s like the motion get “stacked” for every motion before frame (sorry for my English).

This is frame 2, the motion blur gets back to normal:

Cycles has the same effect on frame 1:

How can I get rid of it?

Ok this is a stupid question. The workaround is removing the frame 1 after rendering.