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Class constants and controls have black background when they contain non-default values: Class constants (and controls) always have the default value of their private data control unless you explicitly create a non-standard constant like in the example above. It is updated every time the private data control is changed. This is why VIs containing the class are broken until the changes to the private data control are applied. That is correct. It does not. The default control does not actually contain a copy of the private data control, but a value to indicate that it returns the class default value. Even if you make this value its default value, it is still just a value that indicates that it returns the class default value. Only when the background turns black, you have to worry. By any chance, do you write values to class controls? This can result in undesired situations when combined with 'Make Current Values Default':

UI Element Property Nodes ALWAYS execute in the UI thread. This applies to VI server nodes operating on front panel and control refnums (and almost certainly on diagram refnums too, but this would be pure scripting so if you do anything time critical here, you are definitely operating in very strange territory). CLFN is Call Library Function Node. These calls can be configured to run either reentrant or in the UI thread. If set to run in UI thread and it is a lengthy function (for instance waiting for some event in the external code) it will consume the UI thread and block it for anybody else including your nice happy property nodes! Now don't run and change all CLFN to run reentrant! If the underlaying DLL is not programmed in a way that it is multithreading safe (and quite some are not) you can end up getting all sorts of weird results from totally wrong computations to outright crashes! So your VI may have worked for many years by chance. But as we all had to learn for those to nice to be true earnings from investments, results from the past are no guarantee for the future! 🙂

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