I've modified the standard Contact form and when I published it, I gave it
the same name - IPM.Contact. I open a contact and it still uses the old
form.
Can you not modify the original form?
You can, and sometimes it will work without a hitch, and sometimes it won't.
If it doesn't, then there is a whole ball of wax about clearing cache, and
all the files from some folder. Instructions that I never learned because I
learned how to avoid that whole mess.
The one true cure to the problem is to include the version number in the form
name. That is the only way to force the file system to pull up the right
form, every time. So, your form name should be MyForm_VerNNN, and you
increase that number = NNN every time you publish. So, you can modify the
original form, you just should not republish with the same form name.
Yes, you do wind up with many versions of the same form in the Org Forms
Library, and it will give your Exchange administrator bulimia and the runs,
but you should follow this practice. You use the Forms Manager to delete the
old forms from the Org Forms Library. But make sure that you keep at least
three generations of the form at all times, so that if it one-offs during
your next change cycle, you do not have to start all over again.