I am having the same problem with pk files not being saved when I save the wave file. I too have been using Audition 1.5 for a long time and only recently (maybe this year) has this problem appeared. Don'r know what has changed -- as far as I know I am still opening and saving the same type of file. The properties show it as "32 bit,
Windows PCM, 24-bit Packed Int (type 1 (24-bit))". This is what it always was shown as. Yes I have the save PK checked. (I never unchecked it because I deal with large files and I like PK files.) But now suddenly I have to wait for the entire file to re-draw every time I re-load a file ( a matter of several minutes).
I do notice that it is only the 24 bit files that don't have pk files saved; the 16 bit are fine. So I tried to save as 32 bit and that now does produce a pk file. But Why did it change? I've always used 24 bit files and it used to be OK and I changed no options. And the 32 bit files are 1/3 larger than the 24 bit files (as they should be). I guess I'll live with the extra space as a trade-off for faster loading.