I think the election to the upper chamber of Polish parliament (Senat) in 1989 can be considered such case.

According to the agreements of the Round Table (Okrągły Stół) the lower chamber (Sejm) had an established number of seats (65%) pre-assigned for the governing communist party (PZPR) and their satellites and the remaining MPs were selected in an entirely free election. All those freely elected MPs but 1 were captured by opposing Solidarity (Solidarność) party. Moreover the leading party decided to take only below 40% of MPs giving the rest of the "contingent" to its satellite parties (my guess is they wanted to show a divergence to cool down the anti-communist movement).

Yet all 100 seats in the upper chamber were selected freely.

As a result 99 of senators came from the main opposing party Soladarity with the remaining one place taken by a politician who was independent (but supporting opposition as well). It was a massive loss, unexpected by either of the sides.

The communists decided to accept those results. Annulling them would most probably lead back to massive unrest, strikes, you name it.

Interestingly the opposition managed to convince the satellite parties of PZPR to switch sides. As a result in August 1989 PZPR lost the majority in Polish parliament lower chamber as well effectively closing the communists rule over the Poland. All the upcoming elections (presidential in 1990 and parliamentary in 1991) were completely free and won by the recent opposition (now divergent, with a number of parties).

See this Wikipedia article as a lead in.

I think the election to the upper chamber of Polish parliament (Senat) in 1989 can be considered such case.

According to the agreements of the Round Table (Okrągły Stół) the lower chamber (Sejm) had an established number of seats (65%) pre-assigned for the governing communist party (PZPR) and their satellites and the remaining MPs were selected in an entirely free election. All those freely elected MPs but 1 were captured by opposing Solidarity (Solidarność) party. Moreover the leading party decided to take only below 40% of MPs giving the rest of the "contingent" to its satellite parties (my guess is they wanted to show a divergence to cool down the anti-communist movement).

Yet all 100 seats in the upper chamber were selected freely.

As a result 99 of senators came from the main opposing party Solidarity with the remaining one place taken by a politician who was independent (but supporting opposition as well). It was a massive loss, unexpected by either of the sides.

The communists decided to accept those results. Annulling them would most probably lead back to massive unrest, strikes, you name it.

Interestingly the opposition managed to convince the satellite parties of PZPR to switch sides. As a result in August 1989 PZPR lost the majority in Polish parliament lower chamber as well effectively closing the communists rule over the Poland. All the upcoming elections (presidential in 1990 and parliamentary in 1991) were completely free and won by the recent opposition (now divergent, with a number of parties).

See this Wikipedia article as a lead in.