bROKEN cAPSLOCK kEY fIASCO

05AB1E, 16 bytes

Thanks to Emigna for saving a byte and fixing a bug!

vyÐl'ŒÎ¾èQi¼ëš}?

Explanation:

vy                # For each character in the string...
  Ð               #   Triplicate that character
   l              #   Convert to lowercase
    'ŒÎ           #   Compressed version of "christmas"
       ¾          #   Push the counting variable (let's call this N)
        è         #   Get the nth character of "christmas", with modular indexing
         Qi   }   #   If equal...
           ¼      #      N += 1
            ë     #   Else...
             š    #      Swapcase
               ?  #   Print that character

Uses the CP-1252 encoding. Try it online!

V, 38, 36 bytes

ÄVumaOchristmasòÉf2x`a@"maj~HòHdjV~

Try it online! (contains input and expected output for comparison)

When I first saw this, I thought it would be extremely easy. In fact, if it were not for the "christmas" bug, this would just be 2 bytes: V~. The christmas bug makes it significantly harder, for a very hacky answer.

As usual, here is a hexdump:

00000000: c456 756d 614f 6368 7269 7374 6d61 731b  .VumaOchristmas.
00000010: f2c9 6632 7860 6140 226d 616a 7e48 f248  ..f2x`a@"maj~H.H
00000020: 646a 567e                                djV~

PHP, 113 110 102 bytes

while($o=ord($c=$argv[1][$i++]))echo chr(32|$o==ord(christmas[$k%9])?$o|0&$k++:ctype_alpha($c)*32^$o);

takes input from first command line argument. Run with -r.

breakdown

while($o=ord($c=$argv[1][$i++]))// loop through string characters
    echo chr(
        32|$o==ord(christmas[$k%9]) // if $c equals next character in "christmas"
            ?$o|0&$k++              // no change, increase "christmas" index
            :ctype_alpha($c)        // else if $c is a letter
                    *32^$o          // toggle bit 5 of the ascii code
        );