Why does the word sometimes appear as כַּיּוֹם and sometimes as כְּהַיּוֹם? As a general grammatical rule, a heh with a patach gets subsumed into the preceding kaf, so why are these cases different? Is there a difference in meaning or some sort of pattern? (As far as I know, כְּהַיּוֹם appears only 8 times in Tanach, while כַּיּוֹם appears much more often.)
One example of כְּהַיּוֹם appears in Breishit 39:11. Other examples appear in Devarim 6:24, Shmuel I 9:13, Yirmiyahu 44:22, Ezra 9:7, Ezra 9:15, Nechemia 5:11, and Nechemia 9:10.
For examples of כַּיּוֹם see Breishit 50:20, Devarim 2:30, Devarim 8:18, Shmuel I 22:8 etc.