Constrain proportions checkbox not working properly

[muzzwood]

When editing an image, if I untick 'constrain proportions' then click OK, proportions are still constrained. The only way is to remove both the width and height values.

[VascoVisser]

I can confirm this issue with tinymce Version 4.2.4. Removing the wxh values in the insert/edit dialog doesn't seem to help, the values remain. The workaround for now is removing wxh values from source.