[Plugin: W3 Total Cache] _index_low.html permission problems

I’ve recently installed W3 Total Cache, and it seemed to work like a charm, then I noticed that after a while, in Internet Explorer it starts throwing 403 Access Forbidden error message, whichever the link on my site I try. The error always went away when I switched off the page caching, and came back when I switched it on. When I emptied the page cache, it also started working, then after a while it again stopped.

I’ve been able to trace it down to a permission error on files _index_low.html and _index_low.html.gzip.

Anyway, my _index.html(and gzip) has permission 644 (rw-r–r–), while for some reason _index_low.html (and gzip) has permission 640 (rw-r—–).

When I manually reset the permissions on html and gzip files to 644, again it worked in Internet Explorer.

Strange thing is – after a while, the files either gets deleted and recreated with incorrect permissions, or they just get their permissions reset to 640.

Permissions on all folders, including wp-content, w3tc and others are correctly set to 755.

To me, it seems that there is an error somewhere in code. What would be the reason for permissions to be set at 640, though? Does anyone know of a more permanent solution, other than me watching over the files and manually change permissions as they get reset to 640?

Thanks,

Vjeko