Thanks for the reply. Unfortunately we can't upgrade to PB 12.6 yet. Part of our application is implemented as a COM component which PB 12.6 doesn't support. We have looked at re-writing that as a .Net component, but because we use the Kodigo framework we can't do that either at this stage.
I didn't realise that the PB support was specific to the ASE version. Our clients are using the Open Client 15 libraries and release is set to 15 in the connection.
Some of these applications have been working fine for the last 15 years (since PB 6, then PB 10 and now PB 10.5) with ASE versions 11, 12.5 and 15 without any issues, but for some reason the behaviour is different with ASE 16. I've contacted SAP support and they suggested it could be a holdlock problem, but I don't think PB issues a holdlock with its select statements.
I'll look at using the commit in the idle event as a workaround until we find a proper solution.