The 'descending-ness' bleeds through into other datasessions as well, so just don't do it. Unless you know that the table/cursor in question is not used anywhere else within the current process.

There are other bleed-through issues, like the NOUP vs. SHAR thingy, and these make really nice Heisenbugs (hard to find, tend to disappear when looking) unless you have measures in place to prevent them in the first place. Like a wrapper function around USE that avoids the readonly problem, or a baseball bat in case somebody gets caught using the DESCENDING clause with SET INDEX.