Now I see! The OnStart property was already included in 4.1 build 1275, but a bug in the obfuscation process prevented it from being visible
(actually, it was renamed as LS_Qpu; before you complete the upgrade, you could use the latter name on your code and workaround the problem).

When I tested it last month, I used the non-obfuscated version of the sources and couldn't replicate the problem.
The bug was fixed in 4.1 build 1289, but we forgot to mention the fix in the changelog.
We apologize for this and will fix the changelog.