I could read that in two ways:
If it is the first, then your best bet is to add "post functions" to the "resolve issue" transition that say "clear field X"
If it is either of them, then you want remove the fields from the "resolve issue" screen. Go into the workflow, work out which screen it is using, go to that screen, and remove the fields. For the first possible answer, you're removing them because whatever the user puts in is going to be overwritten by the post-function. For the second possible answer, well, you're removing the field as requested.
Couple of caveats though:
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.