Right. It also looks similar to this:
My guess is that the 'missing ivy jar' problem has existed in both plugins and regular apps for a while. But it only comes to light if there is actually something in your code or a plugin's code that makes reference to ivy classes.
I'm not sure it is worth for me to do a similar 'patchy workaround' in STS specific to Grails 1.3.7 (and 1.3.8?). It won't fix your problem until you upgrade STS Grails support to a version that has my fix (that would likely be 3.0, unless you are ok working from a nightly snapshot.
Since the problem is supposed to be fixed in Grails 2.0.3, depending on how serious this problem is for you maybe you could upgrade your project to 2.0.3 (I realize that may not be trivial
Anyhow, I can certainly and easily broaden the scope of the 'fix' I put in for
STS-2084. Just not sure how useful it would be. (I.e. what I'm saying is that if you think it will actually help you, I will do so, otherwise I'm inclined to close this issue as won't fix).