The method Form>>rotateBy: slows down if applied several times to the same form

Dears, applying the method "Form>>rotateBy:" several times, to the same form, the system slows down dramatically, even imposing a 0° rotation. Below you can find a code snippet, to be run on the playground: |aForm | aForm:= ImageReadWriter formFromFileNamed: 'pharo.png'. 10 timesRepeat: [ aForm := aForm rotateBy:90 ]. Increasing the number of repetitions the delay get worse. Does someone else get the same issue? Is there something wrong on my code, or in the way I'm using the method? The test has been launched in a Pharo 6.0 image, Latest update: #60499, under Linux 64bit. For this question I opened the FogBugz case n°20216 https://pharo.fogbugz.com/f/cases/20216#BugEvent.190469 Thanks, Matteo