You are right, indeed!!
If the table in DE is part of a DBC, you can open the form in design mode even when the table is open exclusively somewhere else! The form opens in design mode, but, of course, if you try to browse the table you get 'File access denied'...

To recap:
A. Table in the DE part of a DBC:
A1. DBC open EXCL - form doesn't open, file access denied error.
A2. Table open EXCL on another WS - MODIFY FORM is slow.
A3. Table open NON EXCL on another WS - MODIFY FORM is fast.
A4. Table open in another VFP session on the same WS - MODIFY FORM is fast, the exclusive open doesn't matter.

B. Table in the DE free table:
B1. Table open EXCL - form doesn't, file access denied error.
B2. Table is open NON EXCL on another WS - MODIFY FORM is slow.
B3. Table is NOT open on any other WS - MODIFY FORM is fast.
B4. Table is open NON EXCL in another VFP session on the same WS - MODIFY FORM is fast.

A2 is a surprise to me, I'd expect that you can not open the form.
B2 is the one that is a problem.
A3/B2 seem to confirm what you say, that vfp team tested only "tables in DBC" situation.

>Yes, it took me some days before I thought to try what I did today - but it was a *very* impressive test. I'm fairly sure it's related to your problem, as I can also get a similar delay by doing a VALI DATA with a DBC open SHARED with tables open multi-user. Here's what you do for the DE test, and it's easiest to test if vfp is on both machines (though you could use an EXE on PC #1, if you wanted):
>
>1) On PC #1:
>
>a) Open vfp.
>b) Type SET EXCL OFF
>c) OPEN (or MODI DATA) any DBCs involved in the DE of the slow MODI FORM
>d) Then type SET EXCL ON
>e) USE some tables that are in the DE (they are now open EXCL, test this with ISEXCL() to be sure).
>
>2) Go to PC #2
>
>a) Issue a MODI FORM on the DE slow form
>b) Form will open veerrryyy slowly (but it *will* open, it's only EXCL DBCs that prevent the DE from opening).
>
>3) Return to PC #1
>
>a) Close all tables (but not the DBCs)
>b) Type SET EXCL OFF
>c) Reopen all tables
>d) Now MODI FORM on PC #2 opens right away, at least for me.
>
>This test is repeatable, and has very clear results showing a serious MODI FORM delay, depending on how many tables are open EXCL on the 2nd machine (at least in my environment). Try it, and you should see what I mean. See if it is similar (in delay) to what you are seeing with your DE and free tables.
>
>If your problem is not quite exactly this, I believe it is related somehow. I haven't used free tables much for a long time, but that could explain the difference in your findings and in mine, and why no one else seems to have noticed this MODI FORM delay - probably most of us use DBCs now, especially when using DEs...
>
>Added note: Perhaps the vfp team testers used mainly DBCs to test things like DEs, so your particular (Free tables, DE, & Modi form) problem may well have been missed, at a guess. You could try putting your free tables in a DBC, and see if the delay-problem goes away.