This bug was fixed in the package musescore - 2.0.2+dfsg-2ubuntu0.1
--------------- musescore (2.0.2+dfsg-2ubuntu0.1) xenial; urgency=medium
* d/p/04-loading-at-startup.patch: Grab patch from upstream to fix persistent "Loading" window at startup with Qt 5.5.0 (LP: #1574432).
-- Logan Rosen <email address hidden> Fri, 03 Jun 2016 20:20:11 -0400
This bug was fixed in the package musescore - 2.0.2+dfsg- 2ubuntu0. 1
--------------- dfsg-2ubuntu0. 1) xenial; urgency=medium
musescore (2.0.2+
* d/p/04- loading- at-startup. patch: Grab patch from upstream to fix
persistent "Loading" window at startup with Qt 5.5.0 (LP: #1574432).
-- Logan Rosen <email address hidden> Fri, 03 Jun 2016 20:20:11 -0400