Fragment not locked - again

I have sent the same question some time ago but could not get any solution.
Maybe this time I will be luckier, especially that I made new observations:

I have a fragmented table in Mnesia of type disc_only_copies. There is a 2GB
size limit for tables of that type, and this table grows continuously with
new data. Because of that I have the code which periodically (weekly) checks
sizes of fragments and adds new fragments (usually just one) if necessary.
The call I use to add a new fragment is:

mnesia:change_table_frag(name, {add_frag, [node()]}).

And it works, till it does not. Right now my table is in a state when any
call to add a new fragment returns

{aborted,{"add_frag: Fragment not locked",12}}

All earlier change_table_frag calls were successful, but it looks like at
certain moment something bad happened and since then adding a new fragment
to the table is not possible. Every time it returns the error message. Is it
a bug in Mnesia? Is there anything I could do to continue adding new
fragments?

Thanks,
Wojtek