@Fergler Yes I can see the problem here as well.
I made a gif of what is happening.
The path (p1) is used as a mask (the black rounded rectangle) , I also draw the same path with
g.drawPath(p1, obj.area, 4);
the white rounded rectangle
As you can see, the mask is not following the scaling but the same path alone does.
@Christoph-Hart this looks like a bug.
maskissue.gif
HiseSnippet 939.3ocsV8taaaCDmzIpX1scnAXO.B4SJ.BtVoo+AXXnoIwtvnwoFQYECnHnflh1lyTjBTzISsneauW6YouA8MX6nnUrbi65fwp9frNd+ti+ti2czC0JJKOWoQ3lWTjwP364EWHMSOdJgKQ8OAguuWNkH3xIYDyTzQEYj7bVBBi25kVH3laiJe97yOhHHRJa4RHzaTbJ6TdJ2rb0gG9JtPzijvtfmVC8AG1mpjGqDp4.c1xqCJiPmQlvNiXg0vCguS2DtQoiMDCKGg29HURQ7T00RG92vy4iDLqPDJFbja4dJQhkw1UQGOkKRFVE14HvKCWlD1xkD9IuA7D9MquLY7fRE9Ksnd9.2XU5s0JzKpN85TidqgR3ZTZaGk1wKlp4YlkZr74td8kFldLAR60ohCKpwe0v6XEfPZZmRlw5oAgarH3Ic5D5Cu16maAY9biufL1+W76Jmvkr1TMChiWJTiHBm+NUol8BYROFSD.1.naqYS34f+5MWRMbkLX2DM45yUFhtHVvSX5cC8GWobRnuZzuum+GZ0p4j14Li6zNv8SN3sDvufpwPEx4LpI.f2l.DwtbqlWQz9YQ.EqBJGGGBUlANDSZOBXj7TRASGXzyY1kyhZSRRNWMWB0AV2RjSDrf2V47214xva9Np126e4C2eozi.oKC8i533HIKSTLfjOKHKpLtJQE5uXWsPXxDGSpH2sC4qmxMLmCsYtxPw5uMjbGX24OZe4NQyKOCpkwfDwqjpQA6dAK2raXmPazTc.4qjmoLrWKC1q0G.F+wV9eopwiWqNq60JgvFqqQssSW+uYXfbd5HlNz+Jh.ReU.gx+U6o7958T0a4otnsFPkrujadcFS90FDfVjhr8eKXE.0T188iK59bkzHNzjcGOaFDUx25i7P+Z+SHFRkW.GBaRFSa3V9iOgcELRz0S2z6DV9LiJqDaZlRZ2dr22ZO+C.C1tUEUe.sfYw72WQjC+z6+ymit8PDX7kJYtfXVcllcP9BEvgxJCRrCKj4bSQ8A8+uMn6+JE2waH2PmtdN1XMbDx9eO33hqGtuW2wigwHKI31d89suO2EffwVF312ADilaO3OadZLL4fxfcWJYBaSAtgs70I2oplHFl9TJ72vyBkQVY7BkQUJQoDpV8Npqn2dAzOTtBvIY4cuM8FXk8itc4dJbe36nzUc0sLb+M0vGsoFdvlZ3i2TCexlZ3S2TCe121P6eW4EyMpTWaCBMXX2xwSXbWIAp.KqVQ+CffzY8m