The command in rencache.c (Command struct + variable length text) was
incorrectly sized. As a result some bites at the end of the command payload
were uninitialized and was causing hash to randomly change forcing the
system to redraw many more areas.
Since the text of the command for DRAW_TEXT commands is written beginning
at the offset of the text field we compute the bare size of the command as
offsetof(Command, text) instead of sizeof(Command).