Ever since around BOINC 7.14(something), BOINC pre-fetches tasks even with a resource share of zero. This is a problem with "race" projects like PrimeGrid. The solution is to just install the earlier version of BOINC. With windows, it's easy. Just go to the BOINC archive site, download the version, install it.

How does one install an earlier version of BOINC with linux? When installed via package manager? It seems to just offer the latest. I need to switch to an earlier version.