Holding a note while an instrument is not in focus then getting LMMS out of focus holds the note until closing the instrument.

To reproduce:
1. Open an instrument.
2. Load an effect in the effect chain and open its controls and focus it.
3. Hold a note using the keyboard.
4. Get LMMS out of focus by minimizing its window or opening another window.
6. Release the note.

Start by reproducing the sequence with an instrument, an effect-chain control, a held keyboard note, and LMMS losing window focus. Trace the keyboard note release and window-focus handling, then verify that releasing the note after focus returns does not leave it held until the instrument closes.

Written by the indexing model from the issue text.