A bit more detail about this issue:

Currently my huggle3.css has this in the default-summary field:

Reverted edits by [[Special:Contributions/$1|$1]] ([[User talk:$1|talk]]) to last revision by $2

When I revert, however, the edit summary is this:

Reverted edits by [[Special:Contributions/$1|$1]] ([[User talk:$1|talk]])

Notably missing the "to last revision by $2" part.

Since f21234e59f07b5a9f61eb75db45e8858a040d3b9 this should work but you will need to use revert-summary-unknown which doesn't support $2 anyway - the reason is that this one is using API rollback and huggle doesn't know to which revision it's going to rollback, mediawiki knows that

If you want to be able to use $2 you would have to change preferences -> use software rollback