Mozart - Piano Concerto No. 14 in E flat, KV 449

"the first movement ventures off from the normal conception of the concerto. Usually, when it comes time for the cadenza at the end of the recapitulation, the soloists will have a cadential trill on the tonic after which the orchestra will play part of the ritornello leading to the I6/4 at which point the soloists performs the cadenza. However, instead of the trill being accompanied by strings, it is interrupted by them on the second beat and ends up resolving to c minor. Shortly thereafter, however, the I6/4 arrives and the cadenza begins and everything continues on as normal."