Randomly unable to upload more than one file

Hello, I’m testing the product, but the most times I am not able to upload 2 file. With 1 file there is no problem but when I try with 2 files the first one is correctly uploaded while the second one rest pending.
I 've Inspected the network traffic with Chrome and I can see that when the second file transfer starts, there is no call to UploadHandler.ashx, and the system starts looping with GetInfoHandler.ashx that always returns 0 in the content response.
You can test the error also on your test page dhtmlx.com/docs/products/dhtmlxVault/index.shtml.
I attach the printscreen of the Chrome Network Inspector.

Same here. Anyone knows how to fix this?

Have you this issue with the latest version?