oop LV 2026 Q3: Packed library with an XControl locks source child classes of a packed base class

[niXController]

Hello together,

since we moved to LV 2026Q3 (from 2023Q3), some of our classes are locked as soon as a certain packed lib is loaded. I'd like to know whether anyone has seen this or has an idea what is going on.

Setup, where i recreated the issue:

• BaseLib.lvlibp : BaseCtrl.lvclass | has a dynamic dispatch method "DoSomething.vi"
• CtrlLib.lvlibp (uses BaseLib.lvlibp) | an XControl whose Init ability calls "DoSomething.vi" on a ChildCtrl object. ChildCtrl.lvclass overrides "DoSomething.vi"
• SrcChild.lvclass: a source class that inherits from BaseLib.lvlibp:BaseCtrl.lvclass

 

Repro:

1. Open Test/Test.lvproj which contains BaseLib.lvlibp and SrcChild.lvclass -> SrcChild is editable.
2. Add Test/CtrlLib.lvlibp to "My Computer" -> SrcChild is locked.

The error message I get on "Why is Library Locked?":

The library is locked for the following reason(s): A vi in the library is reserved in this application instance or another application instance. The containing library is locked.

Nothing else is running and no XControl instance exists on any FP.

 

The execution states after adding CtrlLib.lvlibp:

• Running: Init.vi, Facade.vi, BaseCtrl:DoSomething.vi, the ChildCtrl override and SrcChild.ctl
• Idle: Data.ctl and State.ctl

 

Before CtrlLib.lvlibp is added, everything is idle.

 

Where I stand so far:

• LV 2023Q3 with the identical code does not have this issue. 
• The XControl is required. CtrlLib.lvlibp with only ChildCtrl (XControl removed) does not lock SrcChild.ctl
• Classes without a parent are not affected.
• SuperSecretPrivateSpecialStuff does not matter. I tested with and without it -> same result
• LV 2024 and 2025 are untested.

 

My environment:

• Windows 11 24H2
• LabVIEW 26.3.1f1 64-bit

 

Has anyone seen this problem before and knows what i can do to prevent it?

 

I attached the repro projects in versions 2026Q3 (to show the issue) and 2023Q3 (to show that it worked before). 

Thanks in advance!

ReproCode_LV2026Q3.zip ReproCode_LV2023Q3.zip