I have a character with the Great Weapon Fighting style.  Per the description, a 1 or 2 on a damage roll can be re-rolled, and the new rolls must be used.  Currently when I roll a 1 or 2, those values are not discarded but instead are added to the rerolled values. This increases my damage by 2-4 points whenever I roll 1s or 2s.  Is there a fix or workaround for this?

No. The DDB die roller can't do fancy tricks like that.

THere's at least one browser extension that does that, but it's third-party and sometimes breaks when they update the site.

the DDB roller is currently re-rolling 1s and 2s. If it can’t also discard those 1s or 2s, then re-rolling should also be disabled.  As it stands, it’s rolling too much damage for characters with Great Weapon Fighting.

Quote from ChrisB_Seb >>

the DDB roller is currently re-rolling 1s and 2s. If it can’t also discard those 1s or 2s, then re-rolling should also be disabled.  As it stands, it’s rolling too much damage for characters with Great Weapon Fighting.

 
Check your extensions because the DDB roller does not have the feature to re-roll 1s and 2s. The roller cannot be affected by any feats or any such things. There are extensions, most famously Beyond20, which can affect the rolls but as mentioned previously these extensions are 3rd party.

Ah, it must be Beyond20 then.  I’ll look into that.