Sony Mobile has just certified a new firmware build with version number 14.2.A.1.142 for the Xperia Z1 (C6902, C6903, C6943, C6906), Xperia Z Ultra (C6802, C6833, C6843, C6806) and Xperia Z1 Compact (D5503). This new firmware most likely brings some bug fixes and performance enhancements, given that the small incremental number upgrade from the last firmware (14.2.A.1.136).
Thanks DetmL and schickel!